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P2038 Reductant Injection Air Pressure Sensor "A" Circuit Range / Performance
P2038 Reductant Injection Air Pressure Sensor "A" Circuit Range / Performance is a generic OBD-II diagnostic trouble code indicating that the vehicle's control module has detected that the signal from the reductant injection air pressure sensor "A" is outside the expected range or is not responding correctly to operating conditions.
This code is associated with the Selective Catalytic Reduction (SCR) system found on many modern diesel vehicles. In SCR systems that use compressed air to assist reductant injection, the injection air pressure sensor monitors pressure in the dosing system and sends an electrical signal to the engine control module or aftertreatment control module.
In simple terms, the control module is receiving a pressure-sensor signal that does not behave as expected.
Unlike a specific circuit low or circuit high code, P2038 does not necessarily indicate that the signal is simply too low or too high. The signal may instead be:
-
Outside the expected operating range
-
Incorrect for the current pressure
-
Too slow to respond
-
Erratic
-
Stuck at one value
-
Not changing when pressure changes
-
Changing in a way that does not correspond to the commanded air pressure
Possible causes include:
-
Faulty reductant injection air pressure sensor
-
Damaged sensor wiring
-
Poor electrical connection
-
Incorrect reference voltage
-
Sensor ground problem
-
Air-pressure leaks
-
Restricted air lines
-
Faulty reductant air pump
-
Faulty pressure regulator
-
Faulty pressure-control valve
-
Excessive or insufficient injection-air pressure
-
DEF/AdBlue crystallization
-
Aftertreatment control-module problems
-
Software or calibration issues
Therefore, P2038 should not automatically be diagnosed as a failed pressure sensor.
What Does P2038 Mean?
The code description contains several important terms.
Reductant
"Reductant" refers to the fluid used by an SCR system to reduce nitrogen oxide emissions.
Depending on the vehicle and market, it may be called:
-
Diesel Exhaust Fluid (DEF)
-
AdBlue
-
AUS 32
-
Urea solution
The reductant is injected into the exhaust stream, where it helps the SCR catalyst convert nitrogen oxides into primarily nitrogen and water.
Injection Air Pressure
Some SCR systems use compressed air to assist the reductant injection process.
The compressed air can help:
-
Atomize the reductant
-
Improve spray quality
-
Transport reductant through the dosing system
-
Maintain consistent injection conditions
-
Improve dosing accuracy
The control module therefore needs accurate information about injection-air pressure.
Pressure Sensor "A"
The letter "A" identifies a particular pressure sensor or pressure-sensor circuit within the vehicle manufacturer's SCR system.
It does not necessarily mean that every vehicle uses a component physically labeled "A."
The location and design of the sensor vary between manufacturers.
Range / Performance
The term "Range / Performance" means that the control module has determined that the sensor signal is not behaving as expected, rather than simply detecting a straightforward high or low voltage.
For example, the sensor may show:
-
Correct voltage at one pressure but incorrect voltage at another
-
A signal that does not change when pressure changes
-
An implausible pressure reading
-
Slow sensor response
-
An unstable signal
-
A signal that disagrees with another pressure measurement or expected system condition
This is why P2038 generally requires a broader diagnosis than a simple circuit-high or circuit-low fault.
How Does the Reductant Injection Air Pressure Sensor Work?
Many automotive pressure sensors use a three-wire circuit consisting of:
-
Reference voltage
-
Ground
-
Signal
The sensor converts pressure into a variable electrical signal.
As injection-air pressure changes, the sensor output should change accordingly.
The control module monitors this signal and compares it with:
-
Expected pressure
-
Air-pump operation
-
Pressure-control commands
-
Reductant dosing activity
-
Engine operating conditions
-
Other system information
If the signal does not correspond to the expected pressure or does not respond correctly, P2038 may be stored.
A simplified example is:
Correct pressure → correct sensor signal
Pressure changes → sensor signal changes accordingly
Pressure changes but signal remains fixed → possible sensor or circuit problem
Sensor signal changes incorrectly → possible sensor or wiring problem
Sensor signal is correct but actual pressure is abnormal → possible air-system problem
The exact pressure and voltage specifications are manufacturer-specific.
Why Is Injection Air Pressure Important?
On air-assisted SCR systems, injection-air pressure affects how the reductant is delivered into the exhaust.
Correct pressure can influence:
-
Reductant atomization
-
Spray pattern
-
Dosing accuracy
-
Injector operation
-
SCR catalyst performance
-
NOx conversion efficiency
If the pressure sensor does not provide reliable feedback, the control module may have difficulty determining whether the reductant injection system is operating correctly.
Symptoms of P2038
The symptoms can vary significantly depending on the vehicle and the underlying cause.
Check Engine Light
The Check Engine Light may illuminate when the control module detects an injection-air pressure range or performance problem.
DEF/AdBlue Warning
The vehicle may display messages such as:
-
Check DEF
-
Check AdBlue
-
DEF system fault
-
AdBlue system fault
-
Exhaust fluid system fault
-
SCR system fault
-
Emissions system fault
The exact message depends on the manufacturer.
Unstable Injection-Air Pressure Reading
A scan tool may show a pressure value that:
-
Fluctuates unexpectedly
-
Does not correspond to pump operation
-
Remains fixed
-
Changes too slowly
-
Is implausible compared with operating conditions
Reductant Dosing Problems
An incorrect pressure signal can interfere with the control system's ability to verify or control reductant injection.
Possible symptoms include:
-
Reduced reductant dosing
-
Dosing interruption
-
Incorrect atomization
-
Dosing-system faults
Reduced SCR Efficiency
If reductant is not injected correctly, NOx conversion efficiency can decrease.
Increased NOx Emissions
A malfunctioning SCR dosing system can increase NOx emissions.
Reduced Engine Power
Some diesel vehicles may eventually activate an emissions-related reduced-power strategy if an SCR fault remains unresolved.
DEF/AdBlue Countdown
A persistent SCR fault may cause a countdown or operating restriction on some vehicles.
Possible warnings include:
-
DEF/AdBlue range countdown
-
Speed limitation
-
Reduced-power warning
-
Restart restriction
The exact strategy varies by manufacturer.
No Noticeable Driving Symptoms
The vehicle may drive normally when P2038 first appears.
Because the fault concerns the SCR/reductant system, engine performance may remain normal until the control module determines that the emissions system cannot operate reliably.
Common Causes of P2038
Faulty Reductant Injection Air Pressure Sensor
A defective sensor is one of the most obvious possibilities.
The sensor may produce a signal that:
-
Does not correspond to actual pressure
-
Changes too slowly
-
Becomes unstable
-
Sticks at one value
-
Has incorrect output characteristics
A sensor can therefore pass a basic electrical test while still failing a range/performance test.
Damaged Sensor Wiring
The pressure sensor signal depends on the integrity of the wiring.
Possible problems include:
-
Broken conductors
-
Chafed insulation
-
Melted wiring
-
Corrosion
-
High resistance
-
Intermittent connections
Because SCR components are often located near the exhaust system, heat damage is particularly important.
Poor Electrical Connection
A loose terminal can cause a pressure signal that changes unpredictably.
Possible connector problems include:
-
Loose pins
-
Poor terminal tension
-
Corrosion
-
Moisture
-
Damaged locking mechanism
Incorrect Reference Voltage
Many pressure sensors depend on a stable reference voltage.
If the reference voltage is incorrect, sensor output may no longer correspond correctly to pressure.
Sensor Ground Problem
A poor or unstable sensor ground can cause inaccurate pressure readings.
A voltage-drop test may reveal a ground problem that a simple continuity test does not identify.
Air-Pressure Leak
A leak in the injection-air system can cause actual pressure to differ from the pressure expected by the control module.
Possible leak locations include:
-
Air hoses
-
Fittings
-
Seals
-
Injector connections
-
Pump connections
Restricted Air Line
A restriction can prevent pressure from changing normally.
Possible causes include:
-
Kinked hose
-
Blocked passage
-
Contamination
-
Frozen moisture
-
Damaged hose
-
Incorrect hose routing
Faulty Reductant Injection Air Pump
A weak or malfunctioning pump may not generate the pressure required by the system.
Possible problems include:
-
Weak pump output
-
Motor failure
-
Electrical supply problems
-
Intermittent operation
-
Internal mechanical wear
Faulty Pressure Regulator
A pressure regulator that cannot maintain the correct pressure can cause the sensor reading to fall outside the expected performance range.
Faulty Pressure-Control Valve
A control valve that sticks, leaks, or responds incorrectly can cause abnormal pressure behavior.
DEF/AdBlue Crystallization
DEF/AdBlue can form urea crystals when it dries.
Crystallization around the reductant injector or related passages can interfere with normal dosing.
However, crystallization alone should not automatically be blamed for P2038. The sensor circuit and actual air pressure should still be checked.
Temperature Effects
Injection-air pressure and sensor behavior can be affected by temperature.
Extreme temperatures can influence:
-
Sensor response
-
Air density
-
Pump operation
-
Moisture in air lines
-
Reductant-system behavior
A fault that appears only when the system is cold or hot can therefore provide an important diagnostic clue.
Moisture or Frozen Water in the Air System
Moisture in an air-assisted dosing system can freeze under low-temperature conditions or interfere with pressure control.
This can result in pressure readings that do not follow expected operating behavior.
Faulty Aftertreatment Control Module
In rare cases, the module monitoring the sensor may have an internal problem.
This should normally be considered only after the sensor, wiring, reference voltage, ground, and actual pressure have been verified.
Software or Calibration Problem
A software or calibration issue may cause the control module to incorrectly interpret a pressure signal.
Vehicles Commonly Affected by P2038
P2038 can occur on diesel vehicles equipped with SCR systems that use reductant injection-air pressure monitoring.
Examples may include:
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Ford Super Duty Diesel
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Ford Transit Diesel
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Chevrolet Silverado Duramax
-
GMC Sierra Duramax
-
Ram Heavy Duty Diesel
-
Mercedes-Benz Sprinter Diesel
-
Volkswagen Touareg TDI
-
Volkswagen Transporter
-
Audi Q7 TDI
-
BMW X5 Diesel
-
Peugeot Boxer Diesel
-
Citroën Jumper
-
Fiat Ducato Diesel
-
Iveco Daily
-
Renault Master
-
Opel Movano
This list is not exhaustive.
The exact SCR architecture, sensor arrangement, air-assist system, and control strategy vary between manufacturers and engine versions.
How Is P2038 Diagnosed?
The most important diagnostic question is:
Is the pressure sensor itself producing an incorrect signal, or is the actual injection-air system operating outside its expected range?
P2038 is a range/performance code, so diagnosis should evaluate both the electrical signal and the physical pressure system.
Step 1: Scan for Additional Trouble Codes
Use a suitable diagnostic scan tool to retrieve:
-
Stored codes
-
Pending codes
-
Manufacturer-specific codes
-
Freeze-frame data
Pay particular attention to codes involving:
-
Reductant injection air pressure
-
Reductant air pump
-
Pressure-control valve
-
Reductant injector
-
DEF/AdBlue dosing
-
NOx sensors
-
SCR efficiency
-
Aftertreatment communication
Additional codes may reveal the underlying problem.
Step 2: Review Freeze-Frame Data
Check the conditions under which P2038 was stored.
Useful information may include:
-
Engine RPM
-
Vehicle speed
-
Engine coolant temperature
-
Ambient temperature
-
Battery voltage
-
Reductant temperature
-
Injection-air pressure
-
Air-pump command
-
Reductant dosing command
This can help determine whether the problem occurs during active reductant dosing or under another operating condition.
Step 3: Monitor the Injection-Air Pressure PID
Use a scan tool to monitor the pressure sensor value.
Look for:
-
Fixed pressure readings
-
Sudden jumps
-
Slow changes
-
Pressure values that do not correspond to pump operation
-
Implausible pressure readings
-
Pressure that does not return to the expected level
Compare the reading with manufacturer specifications.
Step 4: Compare Commanded and Measured Pressure
If the diagnostic tool provides both commanded and measured pressure, compare them.
A large difference may indicate:
-
Sensor error
-
Pressure leak
-
Pump problem
-
Regulator problem
-
Control-valve problem
Step 5: Check Sensor Reference Voltage
Using the vehicle wiring diagram, identify the pressure sensor reference circuit.
Measure the reference voltage and verify that it is within manufacturer specification.
An incorrect reference voltage can cause a pressure signal to appear inaccurate even when the sensor itself is functioning.
Step 6: Check Sensor Ground
Verify the sensor ground.
Perform a voltage-drop test where appropriate.
A high-resistance ground can produce an inaccurate signal.
Step 7: Check Sensor Signal
Measure the pressure sensor signal while observing actual system operation.
The signal should change smoothly and correspond to pressure changes.
An output that:
-
Stays fixed
-
Jumps unexpectedly
-
Changes too slowly
-
Does not correspond to pressure
can indicate a sensor or circuit problem.
Step 8: Inspect the Pressure Sensor Connector
Check for:
-
Corrosion
-
Moisture
-
DEF contamination
-
Loose terminals
-
Bent pins
-
Poor terminal tension
-
Damaged connector housing
Step 9: Inspect the Wiring Harness
Follow the harness from the pressure sensor to the relevant control module.
Look for:
-
Chafing
-
Broken conductors
-
Melted insulation
-
Pinched wiring
-
Exposed wires
-
Previous repairs
-
Loose harness clips
Pay special attention to areas near the exhaust.
Step 10: Perform a Wiggle Test
Monitor the pressure signal while carefully moving the wiring harness and connector.
If the signal changes unexpectedly, investigate the wiring and connector.
Step 11: Check Actual Injection-Air Pressure
Use the manufacturer's approved pressure-testing method.
Determine whether actual air pressure changes correctly when the system is commanded.
This is critical because a range/performance fault can result from a sensor that is reporting incorrectly or from a pressure system that is genuinely behaving abnormally.
Step 12: Check the Reductant Air Pump
Verify:
-
Power supply
-
Ground
-
Command signal
-
Pump operation
-
Pressure output
-
Current draw where specified
The pump should produce the pressure required by the system.
Step 13: Check Pressure Regulation
Test the pressure regulator or control valve.
Verify that pressure rises and falls as commanded.
A regulator that responds too slowly or remains stuck can cause a range/performance fault.
Step 14: Inspect Air Lines
Check for:
-
Leaks
-
Kinks
-
Cracks
-
Blockages
-
Loose fittings
-
Contamination
-
Frozen moisture
Step 15: Inspect the Reductant Injector
Check the reductant injector for:
-
DEF/AdBlue crystallization
-
Blockage
-
Damage
-
Incorrect operation
-
Leakage
A restricted injector can affect the pressure behavior of the system.
Step 16: Check for DEF/AdBlue Crystallization
Inspect the dosing system for dried reductant deposits.
If crystallization is present, follow the manufacturer's approved cleaning or component-replacement procedure.
Step 17: Compare Pressure Behavior at Different Operating Conditions
If possible, observe the system:
-
At startup
-
At idle
-
During active dosing
-
After dosing stops
-
At different engine loads
-
At different temperatures
A sensor that works correctly at idle but becomes inaccurate during active dosing may have a range/performance problem.
Step 18: Check Temperature-Related Behavior
Determine whether P2038 occurs:
-
Only when cold
-
Only when hot
-
After extended driving
-
During cold starts
-
In freezing conditions
This can help identify moisture, frozen air lines, sensor drift, or temperature-related electrical faults.
Step 19: Check Manufacturer Technical Information
Look for:
-
Technical Service Bulletins
-
Known sensor failures
-
Wiring problems
-
Connector updates
-
Air-pump problems
-
Pressure-control issues
-
Software updates
Step 20: Check the Aftertreatment Control Module
If the sensor, wiring, air system, pressure control, and connectors all test correctly, investigate the relevant control module.
Module replacement should be considered only after other possible causes have been eliminated.
How to Fix P2038
The correct repair depends on what is causing the pressure signal to fall outside the expected range or performance characteristics.
Replace a Faulty Pressure Sensor
If testing confirms that the sensor output is incorrect despite correct reference voltage, ground, wiring, and actual pressure, replace the reductant injection air pressure sensor.
Repair Damaged Wiring
Repair or replace:
-
Broken wires
-
Chafed insulation
-
Melted wiring
-
Damaged splices
-
Corroded terminals
Protect the repaired harness from heat, vibration, and abrasion.
Repair or Replace the Connector
If the connector has:
-
Corrosion
-
Water intrusion
-
Loose terminals
-
Poor terminal tension
-
Broken locking components
repair or replace it as required.
Repair the Reference Circuit
If the sensor reference voltage is incorrect, repair the reference circuit or associated power supply.
Repair the Sensor Ground
Repair any high-resistance, damaged, or corroded ground connection.
Repair Air Leaks
Replace damaged:
-
Air hoses
-
Fittings
-
Seals
-
Connections
An air leak can prevent the system from producing the pressure expected by the control module.
Repair or Replace the Reductant Air Pump
If the pump cannot generate or maintain the required pressure, repair or replace it according to the manufacturer's procedure.
Repair or Replace the Pressure Regulator
A defective pressure regulator should be repaired or replaced if it causes abnormal pressure behavior.
Repair or Replace the Pressure-Control Valve
If the valve sticks, leaks, or responds incorrectly, repair or replace it.
Repair Restricted Air Lines
Replace hoses or passages that are blocked, kinked, damaged, or contaminated.
Clean or Replace the Reductant Injector
If DEF/AdBlue crystallization or injector contamination affects system pressure, clean or replace the affected component according to manufacturer instructions.
Address Moisture or Frozen Air Lines
If moisture or ice is found in the air system, correct the underlying cause and repair affected components.
Update Control Module Software
If the manufacturer has released a software update addressing P2038, reprogram the applicable control module.
Replace the Aftertreatment Control Module
If the module has a confirmed internal pressure-sensor input or processing fault after all external components and circuits have been tested, replacement may be necessary.
Perform Required Calibration or Initialization
After replacing a pressure sensor, pump, regulator, valve, injector, or control module, the vehicle may require:
-
Pressure-sensor calibration
-
Reductant-system initialization
-
SCR reset
-
Air-pressure system test
-
Dosing-system test
-
Aftertreatment self-test
-
Module programming
The exact procedure is manufacturer-specific.
Clear the Code and Verify the Repair
After completing the repair:
-
Clear P2038.
-
Start the engine.
-
Monitor injection-air pressure.
-
Verify sensor reference voltage.
-
Verify sensor ground.
-
Monitor sensor signal.
-
Command the reductant air system.
-
Observe pressure response.
-
Compare commanded and measured pressure where available.
-
Verify reductant dosing operation.
-
Test-drive the vehicle.
-
Rescan for stored and pending codes.
The repair should be considered successful only when the pressure signal responds correctly to changes in actual pressure and P2038 does not return.
What Happens If P2038 Is Ignored?
If the pressure sensor continues to provide unreliable information, the SCR system may not be able to accurately monitor or control reductant injection.
Possible consequences include:
-
DEF/AdBlue warning
-
SCR system warning
-
Incorrect reductant dosing
-
Reduced dosing
-
Dosing interruption
-
Poor reductant atomization
-
Increased NOx emissions
-
Reduced SCR efficiency
-
Additional aftertreatment fault codes
-
Reduced engine power
-
Speed limitations
-
DEF/AdBlue countdown
-
Restart restrictions on some vehicles
If the actual pressure system is also malfunctioning, continued operation may place additional stress on the air pump, regulator, valve, injector, or related components.
Can You Drive With P2038?
Short-term driving may be possible if the vehicle operates normally, but P2038 should be diagnosed promptly.
The vehicle may initially show only a Check Engine Light or emissions-system warning.
However, unresolved SCR faults can eventually lead to:
-
DEF/AdBlue countdown
-
Reduced engine performance
-
Speed limitation
-
Emissions-system warnings
-
Restart restrictions
If the vehicle is showing a countdown or reduced-power warning, it should be inspected as soon as possible.
Is P2038 a Serious Code?
P2038 is generally considered a moderate-severity emissions-system fault.
It does not normally indicate an immediate mechanical engine failure.
However, the code indicates that the SCR control system cannot reliably determine whether the reductant injection air pressure is behaving correctly.
The severity increases if P2038 is accompanied by:
-
Reductant air-pump faults
-
Reductant injector faults
-
Pressure-control faults
-
NOx sensor faults
-
SCR efficiency faults
-
DEF/AdBlue countdown
-
Reduced-power warnings
The vehicle should therefore be diagnosed before the condition progresses.
P2038 vs. P2039 and P2040
P2038, P2039, and P2040 concern the Reductant Injection Air Pressure Sensor "A", but they describe different types of problems.
| Code | General Meaning |
|---|---|
| P2038 | Reductant Injection Air Pressure Sensor "A" Circuit Range / Performance |
| P2039 | Reductant Injection Air Pressure Sensor "A" Circuit Low |
| P2040 | Reductant Injection Air Pressure Sensor "A" Circuit High |
| P2041 | Reductant Injection Air Pressure Sensor "A" Circuit Intermittent |
The distinction is important.
P2038 indicates that the sensor signal is not behaving correctly within the expected range or performance characteristics.
P2039 indicates a low electrical signal.
P2040 indicates a high electrical signal.
P2041 indicates an intermittent signal.
For P2038, diagnosis should focus on both:
-
Sensor signal plausibility
-
Actual injection-air pressure
For P2039, greater attention should be given to:
-
Signal short to ground
-
Missing reference voltage
-
Sensor failure
-
Wiring problems
-
Low actual pressure
For P2040, greater attention should be given to:
-
Signal short to voltage
-
Sensor failure
-
Ground problems
-
High actual pressure
For P2041, attention should be given to:
-
Loose connectors
-
Broken conductors
-
Corrosion
-
Harness movement
-
Vibration-related faults
-
Intermittent sensor failure
P2038 vs. P2042–P2046
P2038 should not be confused with the reductant temperature sensor codes.
| Code | General Meaning |
|---|---|
| P2038 | Reductant Injection Air Pressure Sensor "A" Circuit Range / Performance |
| P2042 | Reductant Temperature Sensor Circuit Malfunction |
| P2043 | Reductant Temperature Sensor Circuit Range / Performance |
| P2044 | Reductant Temperature Sensor Circuit Low |
| P2045 | Reductant Temperature Sensor Circuit High |
| P2046 | Reductant Temperature Sensor Circuit Intermittent |
Therefore:
P2038 → Injection air pressure sensor "A"
P2042–P2046 → Reductant temperature sensor
The presence of P2038 does not automatically indicate a problem with the DEF/AdBlue temperature sensor.
P2038 vs. P2047–P2049
P2038 also differs from the reductant injection valve circuit codes.
| Code | General Meaning |
|---|---|
| P2038 | Reductant Injection Air Pressure Sensor "A" Circuit Range / Performance |
| P2047 | Reductant Injection Valve Circuit/Open Bank 1 Unit 1 |
| P2048 | Reductant Injection Valve Circuit Low Bank 1 Unit 1 |
| P2049 | Reductant Injection Valve Circuit High Bank 1 Unit 1 |
Therefore:
P2038 → Pressure sensor range/performance
P2047 → Injection valve circuit open
P2048 → Injection valve circuit low
P2049 → Injection valve circuit high
P2038 does not automatically mean that the reductant injector is defective.
How to Prevent P2038
Not every pressure-sensor or electrical failure can be prevented, but proper maintenance can reduce the risk.
Recommended practices include:
-
Inspect SCR wiring during routine servicing.
-
Protect sensor wiring from exhaust heat.
-
Prevent harnesses from rubbing against chassis components.
-
Inspect pressure sensor connectors for corrosion and moisture.
-
Repair damaged air hoses promptly.
-
Inspect air-pump connections.
-
Maintain the SCR air-assist system according to manufacturer recommendations.
-
Address DEF/AdBlue crystallization when discovered.
-
Use the correct DEF/AdBlue specification.
-
Avoid unnecessary modifications to SCR wiring.
-
Address emissions-system warnings promptly.
-
Inspect the SCR system after exhaust or underbody repairs.
-
Pay attention to recurring faults that appear only during cold or hot conditions.
Final Thoughts
P2038 Reductant Injection Air Pressure Sensor "A" Circuit Range / Performance indicates that the vehicle's control module has detected that the injection-air pressure sensor signal is not behaving within the expected range or performance characteristics.
The important difference between P2038 and simple circuit-high or circuit-low codes is that P2038 does not necessarily mean that the electrical signal is simply too high or too low.
The signal may instead be:
-
Implausible
-
Slow to respond
-
Erratic
-
Stuck
-
Incorrect for the actual pressure
-
Incorrect for the commanded pressure
-
Outside the expected operating characteristics
Possible causes include:
-
Faulty pressure sensor
-
Damaged wiring
-
Poor connector connection
-
Incorrect reference voltage
-
Sensor ground problem
-
Air leaks
-
Restricted air lines
-
Weak or failed reductant air pump
-
Pressure-regulator problems
-
Pressure-control valve problems
-
DEF/AdBlue crystallization
-
Moisture or frozen air lines
-
Temperature-related sensor or system problems
-
Aftertreatment control-module faults
-
Software or calibration problems
The most important diagnostic step is to determine whether the sensor signal is wrong or whether the actual injection-air pressure is behaving incorrectly.
If actual pressure is normal but the sensor signal is implausible, attention should shift toward the pressure sensor, reference voltage, ground, signal circuit, wiring, and connector.
If the sensor accurately reflects an abnormal pressure condition, the technician should investigate the reductant air pump, pressure regulator, control valve, air lines, injector, and other components responsible for pressure generation and control.
The pressure sensor should not automatically be replaced simply because P2038 is stored.
Once the underlying cause has been identified, the repair may involve sensor replacement, wiring or connector repair, air-pump repair, pressure-regulator or control-valve replacement, air-line repair, removal of DEF/AdBlue crystallization, or control-module programming.
After the repair, the code should be cleared and the SCR system tested under the operating conditions in which the fault originally occurred.
A successful repair should result in a pressure-sensor signal that changes appropriately with actual injection-air pressure, remains within the manufacturer's specified operating characteristics, and does not cause P2038 to return.
