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P2045 Reductant Temperature Sensor Circuit High
P2045 Reductant Temperature Sensor Circuit High is a generic OBD-II diagnostic trouble code indicating that the Engine Control Module (ECM), Powertrain Control Module (PCM), or aftertreatment control module has detected a higher-than-expected electrical signal from the reductant temperature sensor circuit.
In simple terms, the vehicle's computer is receiving an abnormally high voltage or electrical value from the sensor that monitors the temperature of the reductant fluid, such as Diesel Exhaust Fluid (DEF) or AdBlue.
The reductant temperature sensor is part of the Selective Catalytic Reduction (SCR) system used on many modern diesel vehicles. The sensor provides temperature information that helps the control system manage reductant heating, pumping, dosing, and freeze protection.
Despite the code referring to a "high" circuit signal, P2045 does not necessarily mean that the DEF/AdBlue itself is too hot. The fault can be caused by an electrical problem such as an open signal circuit, poor sensor ground, damaged wiring, high resistance, or a failed temperature sensor.
This distinction is important because replacing the temperature sensor without testing the circuit may not solve the problem.
What Does P2045 Mean?
The code description contains several important terms.
Reductant
Reductant is the fluid used by an SCR system to reduce nitrogen oxide (NOx) emissions.
On most applicable diesel vehicles, the reductant is:
-
Diesel Exhaust Fluid (DEF)
-
AdBlue
-
A urea-based solution
DEF/AdBlue is injected into the exhaust, where it contributes to the chemical process used by the SCR catalyst to reduce NOx.
Temperature Sensor
The reductant temperature sensor measures the temperature of the DEF/AdBlue or the temperature within the reductant tank/module.
The control module uses this information to determine the thermal condition of the reductant system.
This can affect:
-
Reductant heating
-
Pump operation
-
Injection strategy
-
Freeze protection
-
SCR operation
-
System diagnostics
Circuit
The circuit can include:
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Reductant temperature sensor
-
Signal wire
-
Reference-voltage circuit
-
Ground circuit
-
Electrical connector
-
Wiring harness
-
Reductant tank module
-
Aftertreatment control module
-
ECM/PCM, depending on vehicle design
A fault anywhere in this circuit can cause the control module to detect a high signal.
High
"High" means the control module sees an electrical signal above the expected range.
With many temperature-sensor designs, particularly NTC thermistors, an unusually high signal can be associated with:
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An open circuit
-
Missing sensor ground
-
Broken signal wire
-
High-resistance connection
-
Disconnected connector
-
Failed sensor
The exact electrical interpretation depends on the vehicle's sensor design.
How Does the Reductant Temperature Sensor Work?
Many reductant temperature sensors use an NTC thermistor.
An NTC thermistor generally behaves as follows:
-
Temperature rises → resistance decreases
-
Temperature falls → resistance increases
The control module uses the sensor's electrical characteristics to calculate temperature.
A simplified example is:
Low temperature → higher sensor resistance → higher sensor signal
High temperature → lower sensor resistance → lower sensor signal
This is why a high sensor signal can sometimes indicate a very cold temperature or an open circuit, rather than an overheated DEF tank.
The exact voltage and resistance values vary by manufacturer.
Why Does P2045 Occur?
The control module continuously monitors the reductant temperature signal.
If the measured signal exceeds a calibrated threshold, the control module can determine that the signal is implausible or electrically abnormal and store P2045.
For example, an open sensor circuit can prevent the expected electrical path from being completed. Depending on the circuit design, this can cause the signal voltage to rise toward the reference voltage.
The control module then interprets the signal as "circuit high."
Symptoms of P2045
Symptoms vary depending on the vehicle and whether the fault is currently active.
Check Engine Light
The Check Engine Light may illuminate after the control module detects the high reductant temperature sensor signal.
DEF/AdBlue Warning
The vehicle may display a warning 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 varies by manufacturer.
Implausible Reductant Temperature Reading
A scan tool may show an unrealistic reductant temperature.
For example, the system may report a temperature that is:
-
Extremely low
-
Extremely high
-
Outside the physical range expected for the vehicle
-
Unchanged when the actual temperature changes
If the temperature reading is dramatically different from the ambient conditions, the sensor circuit should be investigated.
Reductant Heater Problems
The control module may have difficulty determining when to activate or deactivate reductant heating.
Possible results include:
-
Heater not operating correctly
-
Incorrect heater activation
-
Longer system warm-up
-
Additional heater-related fault codes
SCR System Problems
An incorrect reductant temperature signal can affect SCR system control.
The vehicle may subsequently store additional codes related to:
-
Reductant dosing
-
Reductant pressure
-
SCR efficiency
-
NOx sensors
-
Reductant heating
Reduced Engine Power
Some diesel vehicles can enter a reduced-power strategy when persistent SCR or emissions-system faults are detected.
DEF/AdBlue Countdown
Depending on the vehicle, a persistent emissions-system fault may trigger a countdown or operating restriction.
The exact strategy is manufacturer-specific.
No Noticeable Driving Problems
P2045 may initially have little or no effect on normal engine operation.
The vehicle may continue to drive normally while the SCR system warning remains active.
However, the fault should still be diagnosed because emissions-system restrictions may occur later.
Common Causes of P2045
Open Temperature Sensor Circuit
An open circuit is one of the most important possibilities when diagnosing P2045.
Possible causes include:
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Broken signal wire
-
Disconnected connector
-
Failed sensor
-
Broken ground wire
-
Damaged internal tank wiring
Disconnected Sensor Connector
A disconnected connector can cause the sensor signal to rise to an abnormal level depending on the circuit design.
Check whether the connector is:
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Fully seated
-
Properly locked
-
Damaged
-
Contaminated
-
Properly sealed
Broken Signal Wire
A broken signal wire can leave the control module's input circuit without the expected sensor signal.
Depending on the circuit configuration, the input can then rise toward the reference voltage.
Poor Sensor Ground
A missing or high-resistance sensor ground can cause the signal voltage to become abnormal.
Possible causes include:
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Corroded ground terminal
-
Broken ground wire
-
Loose connection
-
Internal wiring failure
Damaged Wiring Harness
The reductant system is usually mounted underneath or near the vehicle chassis.
The wiring may be exposed to:
-
Road debris
-
Water
-
Salt
-
Vibration
-
Exhaust heat
-
Abrasion
A damaged harness can create a high signal.
Corroded Connector Terminals
Corrosion can increase resistance or interrupt the sensor circuit.
Inspect for:
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Green corrosion
-
White deposits
-
Rust
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Moisture
-
Loose pins
-
Bent terminals
-
Damaged seals
Water Intrusion
Water entering the connector can cause abnormal electrical readings.
This is especially relevant on vehicles exposed to:
-
Rain
-
Snow
-
Road salt
-
Pressure washing
-
Water crossings
Faulty Reductant Temperature Sensor
The sensor itself may have an internal electrical failure.
Possible failures include:
-
Internal open circuit
-
Incorrect resistance
-
Signal instability
-
Internal connection failure
If the sensor resistance does not match the manufacturer's temperature/resistance specification, the sensor may need replacement.
Faulty Reductant Tank Module
On some vehicles, the temperature sensor is integrated into the DEF/AdBlue tank module.
In such cases, the sensor may not be separately replaceable.
A tank module may need replacement if its integrated temperature-sensor circuit is confirmed defective.
Internal Tank Wiring Problem
Some reductant tanks contain internal wiring connecting the temperature sensor to the external connector.
An internal open connection can be difficult to detect without following the manufacturer's diagnostic procedure.
Reference Voltage Problem
If the reference voltage supplied to the sensor is abnormal, the sensor signal may also be abnormal.
A shared reference circuit fault can affect more than one sensor.
High-Resistance Connection
A poor electrical connection can produce abnormal voltage behavior.
Potential locations include:
-
Connector terminals
-
Splices
-
Ground points
-
Harness junctions
-
Module connectors
DEF/AdBlue Freezing
DEF freezes at approximately −11°C (12°F).
Cold or frozen DEF can affect reductant-system operation, but freezing itself is not automatically a sensor fault.
In fact, the temperature sensor is supposed to report cold conditions so that the system can apply its appropriate heating strategy.
DEF Crystallization
Dried DEF can form white crystalline deposits around reductant components.
Crystallization may affect the injector or other components, but it does not automatically explain a temperature sensor circuit high code.
The electrical circuit should be tested first.
Faulty Control Module
In rare cases, the ECM, PCM, or aftertreatment control module may have an internal problem affecting the sensor input.
This should be considered only after the sensor and wiring have been proven good.
Software or Calibration Problem
A software or calibration issue can occasionally cause incorrect sensor interpretation.
Vehicles Commonly Affected by P2045
P2045 can occur on diesel vehicles equipped with SCR and reductant temperature monitoring.
Examples may include:
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Ford F-250 Super Duty
-
Ford F-350 Super Duty
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Ford F-450 Super Duty
-
Ford Transit Diesel
-
Chevrolet Silverado Duramax
-
Chevrolet Express Diesel
-
GMC Sierra Duramax
-
GMC Savana Diesel
-
Ram 2500
-
Ram 3500
-
Mercedes-Benz Sprinter
-
Volkswagen Touareg TDI
-
Volkswagen Transporter
-
Audi Q7 TDI
-
BMW X5 Diesel
-
Peugeot Boxer Diesel
-
Citroën Jumper
-
Fiat Ducato Diesel
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Iveco Daily
-
Renault Master
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Opel Movano
This list is not exhaustive.
The exact sensor location varies by manufacturer. In some vehicles, the reductant temperature sensor is integrated into the DEF/AdBlue tank module rather than being a separately accessible component.
How Is P2045 Diagnosed?
P2045 should be approached primarily as an electrical high-signal fault.
The diagnostic goal is to determine why the temperature-sensor signal is higher than expected.
Step 1: Scan for Additional Trouble Codes
Use a suitable diagnostic scan tool and retrieve:
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Stored codes
-
Pending codes
-
Manufacturer-specific codes
-
Freeze-frame data
Look for related codes involving:
-
Reductant temperature
-
Reductant heater
-
DEF/AdBlue level
-
Reductant pressure
-
Reductant pump
-
NOx sensors
-
SCR efficiency
-
Aftertreatment communication
Multiple related codes can indicate a shared wiring or power-supply problem.
Step 2: Check Freeze-Frame Data
Review the operating conditions when P2045 was stored.
Useful parameters include:
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Engine RPM
-
Vehicle speed
-
Engine coolant temperature
-
Ambient temperature
-
Reductant temperature
-
Battery voltage
-
Reductant level
-
Reductant pressure
-
Heater status
This can help determine whether the fault occurred during cold start, warm operation, or another specific condition.
Step 3: Check the Reductant Temperature PID
Monitor the reductant temperature with a scan tool.
Compare the displayed value with:
-
Ambient temperature
-
DEF/AdBlue tank temperature
-
Expected temperature change during operation
If the scan tool reports an obviously impossible temperature, investigate the sensor circuit.
Step 4: Inspect the Connector
Locate the reductant temperature sensor or tank module connector.
Check for:
-
Disconnection
-
Corrosion
-
Water
-
Bent pins
-
Loose terminals
-
Damaged locking mechanism
-
Damaged seals
A connector problem is a common cause of high sensor signals.
Step 5: Inspect the Wiring
Follow the harness from the reductant tank toward the control module.
Look for:
-
Broken wires
-
Chafing
-
Melted insulation
-
Pinched wires
-
Exposed conductors
-
Poor previous repairs
-
Loose harness clips
Pay particular attention to sections close to the exhaust system.
Step 6: Check the Reference Voltage
Using the manufacturer's diagnostic procedure, measure the reference voltage at the sensor.
A stable reference voltage is required for correct sensor operation.
If the reference voltage is missing or incorrect, investigate the related circuit.
Step 7: Check the Sensor Ground
Verify that the sensor ground is present and stable.
A voltage-drop test can help identify a poor ground that may not be obvious from a simple continuity test.
Step 8: Check the Signal Voltage
Measure the temperature sensor signal.
A high signal can indicate:
-
Open sensor circuit
-
Disconnected sensor
-
Broken signal wire
-
Missing ground
-
Failed sensor
-
High-resistance connection
Compare the measured value with the manufacturer's specifications.
Step 9: Check Sensor Resistance
If the sensor is separately serviceable and a resistance specification is available, disconnect the sensor and measure its resistance.
Compare the measurement with the specified resistance for the actual reductant temperature.
Possible results include:
Infinite resistance
May indicate an open sensor or circuit.
Very high resistance
May indicate a sensor problem or circuit resistance issue.
Resistance outside specification
May indicate a failed temperature sensor.
The exact resistance values are vehicle-specific.
Step 10: Check for an Open Circuit
Test continuity through the sensor circuit according to manufacturer procedures.
Check the:
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Signal wire
-
Ground wire
-
Reference circuit
-
Harness
-
Connector terminals
An open wire should be repaired rather than simply replacing the sensor.
Step 11: Check for High Resistance
A circuit can have continuity and still have excessive resistance.
Check for high resistance at:
-
Connector terminals
-
Splices
-
Ground connections
-
Harness sections
Voltage-drop testing can help identify these problems.
Step 12: Perform a Wiggle Test
Monitor the sensor signal while carefully moving the harness and connectors.
If the signal suddenly changes, the problem may be an intermittent:
-
Wire break
-
Loose terminal
-
Connector
-
Internal connection
Although P2045 describes a high signal rather than an intermittent fault, wiring movement can expose the source of the abnormal reading.
Step 13: Check the Reductant Heater
If the system uses a reductant heater, verify that the heater operates correctly.
Check whether there are related heater codes.
A shared electrical problem may affect both the temperature sensor and heater system.
Step 14: Check the Tank Module
If the sensor is integrated into the DEF/AdBlue tank module, test the module according to manufacturer specifications.
Some systems require replacement of the entire tank module if the integrated sensor is defective.
Step 15: Check Control-Module Wiring
Verify continuity between the sensor/tank module and the appropriate control module.
Check for:
-
Open circuit
-
Short to ground
-
Short to battery
-
High resistance
-
Poor connector contact
Step 16: Check the Control Module
If the sensor, connector, wiring, reference voltage, and ground all test correctly, investigate the ECM/PCM or aftertreatment control module.
A failed input circuit is possible, but it should be considered only after external causes have been eliminated.
Step 17: Check Manufacturer Technical Information
Look for manufacturer-specific:
-
Technical Service Bulletins
-
Wiring updates
-
Connector problems
-
Tank-module issues
-
Software updates
-
Calibration procedures
How to Fix P2045
The correct repair depends on the cause of the high sensor signal.
Repair a Broken Wire
Repair or replace the damaged section of wiring.
Make sure the repaired harness is:
-
Properly insulated
-
Correctly routed
-
Properly secured
-
Protected from heat and abrasion
Repair or Replace the Connector
If the connector or terminals are damaged, replace the applicable components.
Pay particular attention to terminal tension and water sealing.
Repair the Sensor Ground
Repair:
-
Broken ground wires
-
Corroded grounding points
-
Loose terminals
-
High-resistance connections
Repair the Reference Circuit
If the reference voltage is incorrect because of a wiring problem, repair the associated circuit.
Replace the Reductant Temperature Sensor
If testing confirms that the sensor is defective and it is separately serviceable, replace it with the correct part.
Replace the Reductant Tank Module
If the temperature sensor is integrated into the DEF/AdBlue tank module and cannot be replaced separately, the applicable module may require replacement.
Repair Internal Tank Wiring
If the internal wiring is damaged and the manufacturer provides a repair procedure, repair it according to the service instructions.
Repair the Control Circuit
Repair any:
-
Open circuit
-
Short circuit
-
High-resistance connection
-
Damaged harness
between the sensor and control module.
Repair or Replace the Control Module
If the sensor and wiring are confirmed good but the control module has a faulty temperature-sensor input, the relevant module may need repair or replacement.
Update Control Module Software
If the manufacturer has released software addressing the fault, update the applicable control module.
Perform Required Calibration
After replacing a reductant temperature sensor, tank module, or control module, the vehicle may require:
-
DEF system initialization
-
Reductant level reset
-
Temperature-sensor calibration
-
Tank-module programming
-
SCR system reset
-
Aftertreatment self-test
The exact procedure depends on the vehicle.
Clear the Code and Verify the Repair
After the repair:
-
Clear P2045.
-
Start the vehicle.
-
Monitor reductant temperature.
-
Verify that the temperature reading is physically plausible.
-
Check the sensor signal.
-
Verify reference voltage and ground.
-
Test reductant heater operation if applicable.
-
Drive the vehicle under appropriate operating conditions.
-
Rescan for stored and pending codes.
The repair should be considered successful only when the sensor signal remains within the expected range and P2045 does not return.
What Happens If P2045 Is Ignored?
If the control module cannot trust the reductant temperature signal, it may not correctly manage the SCR system.
Possible consequences include:
-
DEF/AdBlue warnings
-
Incorrect reductant heating
-
Incorrect dosing strategy
-
Reduced SCR efficiency
-
Increased NOx emissions
-
Additional aftertreatment codes
-
Reduced engine power
-
Speed restrictions
-
Restart restrictions on some vehicles
A vehicle may initially continue operating normally, but the problem can become more significant if the fault remains unresolved.
Can You Drive With P2045?
Short-term driving may be possible if the vehicle is operating normally, but P2045 should be diagnosed promptly.
The vehicle may initially show only a Check Engine Light or DEF/AdBlue warning.
However, continued operation can result in additional SCR warnings or operating restrictions on some vehicles.
If the vehicle displays a:
-
DEF/AdBlue countdown
-
Reduced-power warning
-
Emissions-system warning
-
Speed limitation
the vehicle should be inspected as soon as possible.
Is P2045 a Serious Code?
P2045 is generally considered a moderate-severity emissions-system fault.
The immediate issue is an abnormally high electrical signal from the reductant temperature sensor circuit.
The important point is that "high circuit" does not necessarily mean high reductant temperature.
A disconnected connector, broken signal wire, open sensor, poor ground, or high-resistance connection can all produce a high signal depending on the circuit design.
If the fault is ignored, it can interfere with:
-
Reductant heating
-
SCR dosing
-
NOx reduction
-
Emissions control
-
System diagnostics
The severity increases if the vehicle begins displaying reduced-power or operating-restriction warnings.
P2044 vs. P2045 vs. P2046
These three codes describe different conditions involving the reductant temperature sensor circuit.
| Code | General Meaning |
|---|---|
| P2044 | Reductant Temperature Sensor Circuit Low |
| P2045 | Reductant Temperature Sensor Circuit High |
| P2046 | Reductant Temperature Sensor Circuit Intermittent |
P2044 — Circuit Low
The control module detects a signal below the expected range.
Possible causes include:
-
Short to ground
-
Low signal voltage
-
Faulty sensor
-
Wiring problem
P2045 — Circuit High
The control module detects a signal above the expected range.
Possible causes include:
-
Open circuit
-
Disconnected connector
-
Broken signal wire
-
Missing ground
-
High-resistance connection
-
Faulty sensor
P2046 — Circuit Intermittent
The sensor signal becomes unstable or temporarily disappears.
Possible causes include:
-
Loose connector
-
Broken conductor
-
Chafed wiring
-
Corroded terminal
-
Internal sensor fault
-
Intermittent power or ground
The sequence can therefore be remembered as:
-
P2044 → Low
-
P2045 → High
-
P2046 → Intermittent
P2045 vs. P2047, P2048 and P2049
The following codes move from the reductant temperature sensor to the reductant injection valve circuit.
| Code | General Meaning |
|---|---|
| P2045 | Reductant Temperature Sensor Circuit High |
| 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 |
The distinction is important.
P2045 concerns the reductant temperature sensor circuit.
P2047 concerns an open reductant injection-valve circuit.
P2048 concerns a low reductant injection-valve circuit.
P2049 concerns a high reductant injection-valve circuit.
Therefore, P2045 should not automatically lead to replacement of the DEF injector. The diagnostic focus should remain on the temperature sensor and its electrical circuit.
How to Prevent P2045
Not every electrical fault can be prevented, but proper maintenance can reduce the risk.
Recommended practices include:
-
Inspect reductant-system wiring during servicing.
-
Repair damaged harnesses promptly.
-
Keep DEF/AdBlue connectors properly sealed.
-
Protect wiring from exhaust heat and abrasion.
-
Avoid damaging the DEF/AdBlue tank.
-
Maintain the battery and charging system.
-
Use the correct DEF/AdBlue specification.
-
Address DEF and emissions warnings promptly.
-
Avoid unnecessary modifications to aftertreatment wiring.
-
Inspect wiring after exhaust or tank repairs.
-
Follow manufacturer procedures after tank-module replacement.
Final Thoughts
P2045 Reductant Temperature Sensor Circuit High indicates that the vehicle's control system has detected an electrical signal from the reductant temperature sensor circuit that is higher than the expected range.
The most common possibilities include:
-
Open sensor circuit
-
Disconnected connector
-
Broken signal wire
-
Missing or poor sensor ground
-
Corroded terminals
-
Damaged wiring harness
-
High-resistance connection
-
Faulty reductant temperature sensor
-
Faulty reductant tank module
-
Reference-voltage problems
-
Control-module faults
-
Software or calibration issues
The most important diagnostic point is that P2045 does not necessarily mean the DEF/AdBlue is overheating.
With many NTC-based temperature sensors, a high electrical signal can actually result from high sensor resistance or an open circuit. Therefore, a broken wire or disconnected connector can produce P2045 even when the reductant itself is cold.
Diagnosis should begin by checking the live reductant temperature reading and inspecting the sensor connector and wiring. The reference voltage, sensor ground, signal voltage, continuity, and sensor resistance should then be tested against the manufacturer's specifications.
If the sensor is integrated into the DEF/AdBlue tank module, the complete module may need to be replaced, but only after testing confirms that the integrated sensor or internal circuit is defective.
Ignoring P2045 can eventually lead to DEF/AdBlue warnings, incorrect reductant heating or dosing, reduced SCR efficiency, increased NOx emissions, reduced engine power, and operating restrictions.
The correct repair is to identify the source of the high sensor signal, repair the wiring or connector or replace the confirmed defective sensor/module, perform any required calibration, clear the code, and verify that the reductant temperature reading remains stable and physically plausible.
