P0948 Hydraulic Pump Relay/Control Circuit High

The P0948 trouble code is an OBD-II diagnostic trouble code related to the electrical control system of a transmission's hydraulic pump.

P0948 – Hydraulic Pump Relay/Control Circuit High

This code means that the Transmission Control Module (TCM) or another transmission control system has detected an electrical signal that is higher than expected in the hydraulic pump relay or control circuit.

In simple terms, the transmission computer is detecting an abnormal high electrical condition in the circuit that controls the transmission hydraulic pump.

Depending on the transmission design, the pump may be mechanically driven, electrically driven, or part of an electro-hydraulic system. P0948 is especially relevant to transmissions that use an electronically controlled hydraulic pump or pump relay.

The fault can be caused by a relay, wiring, connector, power supply, control circuit, pump motor, fuse or control module.

Importantly, P0948 does not automatically mean that the hydraulic pump itself has failed.

What Does P0948 Mean?

P0948 – Hydraulic Pump Relay/Control Circuit High

An automatic transmission requires hydraulic pressure to operate various internal components.

Hydraulic pressure may be used to control:

• Clutch packs

• Brakes

• Valve bodies

• Shift mechanisms

• Pressure-control systems

• Gear engagement

In electronically controlled transmissions, the hydraulic pump may be controlled directly or indirectly by an electronic system.

A simplified system can be represented as:

TCM → Pump control circuit → Relay/control device → Hydraulic pump → Hydraulic pressure

When the control module detects a voltage or electrical condition above the expected specification in this circuit, it can store P0948.

What Does “Circuit High” Mean?

The word “High” refers to the electrical condition of the circuit, not necessarily high transmission hydraulic pressure.

P0948 does not directly mean:

• High transmission fluid pressure

• Excessive transmission fluid level

• High transmission temperature

• High engine RPM

Instead, it means the control module has detected an electrical signal or voltage higher than the expected value.

A circuit-high condition can be caused by:

• Short to voltage

• Incorrect wiring

• Faulty relay

• Control circuit failure

• Incorrect electrical resistance

• Internal pump electrical fault

• Control-module problem

The exact cause depends on the vehicle's electrical architecture.

What Is the Transmission Hydraulic Pump?

The hydraulic pump is responsible for generating or maintaining the fluid pressure required for transmission operation.

In a conventional automatic transmission, the pump is commonly driven mechanically by the engine through the transmission.

In some newer transmission designs, an electric auxiliary or main hydraulic pump may be controlled electronically.

Electric pumps can be used for purposes such as:

• Maintaining hydraulic pressure

• Supporting stop-start operation

• Providing pressure when the engine is stopped

• Supporting hybrid systems

• Assisting clutch operation

• Supporting electro-hydraulic transmissions

Because transmission designs differ, the exact meaning of the pump-control circuit can vary.

Does P0948 Mean the Hydraulic Pump Is Bad?

Not necessarily.

This is one of the most important points when diagnosing P0948.

The code identifies a problem with the relay/control circuit, not necessarily a failed pump.

Possible causes include:

• Faulty pump relay

• Short to battery voltage

• Damaged wiring

• Incorrect power supply

• Corroded connector

• Faulty pump motor

• Internal pump wiring problem

• Failed control module

The pump should therefore not be replaced before the electrical circuit is tested.

Symptoms of P0948

Symptoms depend on the transmission design and the severity of the electrical fault.

Possible symptoms include:

• Check Engine Light

• Transmission warning light

• Harsh shifting

• Delayed gear engagement

• Delayed Drive or Reverse engagement

• Transmission slipping

• Limited gear operation

• Limp mode

• Loss of certain gears

• Transmission overheating

• Hydraulic pump noise

• Pump not operating

• Vehicle refusing to move

Some vehicles may initially continue operating normally if the transmission has another source of hydraulic pressure or a backup strategy.

Common Causes of P0948

Faulty hydraulic pump relay

If the hydraulic pump is controlled through a relay, a defective relay can cause abnormal circuit voltage.

Possible relay problems include:

• Contacts sticking

• Internal short

• Incorrect switching

• Burned contacts

• Internal coil failure

The relay should be tested according to the manufacturer's specifications.

Short to voltage

A short between the pump-control wire and a power supply can create a circuit-high condition.

Possible sources include:

• Battery voltage

• Ignition voltage

• Another powered circuit

Damaged insulation is a common reason for this type of problem.

Damaged wiring

The pump wiring harness can become damaged through:

• Chafing

• Heat exposure

• Pinching

• Mechanical impact

• Previous repairs

• Corrosion

A wire touching another power circuit can produce a high-signal fault.

Faulty electrical hydraulic pump

If the transmission uses an electric hydraulic pump, an internal electrical fault in the pump motor can affect the control circuit.

Possible problems include:

• Motor winding failure

• Internal short

• Excessive current draw

• Internal connector damage

• Pump controller failure

However, electrical testing should be performed before condemning the pump.

Corroded or damaged connector

Moisture or contamination can affect the pump connector or relay connector.

Inspect for:

• Corrosion

• Bent terminals

• Loose terminals

• Water intrusion

• Damaged connector locks

Faulty fuse or power-distribution component

The pump circuit may share a power-distribution system with other transmission components.

A fuse, power-distribution module or related electrical component can contribute to the fault.

Poor ground

Although P0948 is a circuit-high code, the complete electrical circuit still needs to be inspected, including ground connections.

A poor ground can cause abnormal voltage readings or incorrect pump-control behavior.

Control module fault

The TCM may be unable to control the pump correctly.

A control-module fault should generally be considered only after the external circuit and pump have been tested.

Can Low Transmission Fluid Cause P0948?

Low transmission fluid does not normally cause P0948 directly.

However, low fluid can create serious transmission hydraulic problems.

Low fluid may cause:

• Pump cavitation

• Low hydraulic pressure

• Slipping

• Delayed engagement

• Noise

• Transmission overheating

These conditions can occur at the same time as an electrical pump-control problem, but low fluid itself does not normally create a circuit-high electrical fault.

The fluid level should nevertheless be checked during diagnosis.

Can Dirty Transmission Fluid Cause P0948?

Dirty or contaminated transmission fluid can affect:

• Pump operation

• Valve-body operation

• Hydraulic pressure

• Solenoid operation

• Clutch engagement

However, contaminated fluid does not normally cause an electrical circuit to become high.

If P0948 is stored, the electrical control circuit should be investigated in addition to checking the fluid condition.

P0948 vs. P0947

These two codes identify opposite electrical conditions.

P0947 – Hydraulic Pump Relay/Control Circuit Low

The control module detects an electrical signal or voltage lower than expected.

P0948 – Hydraulic Pump Relay/Control Circuit High

The control module detects an electrical signal or voltage higher than expected.

This distinction can help direct the diagnostic process.

With P0948, particular attention should be given to short-to-voltage conditions and abnormal power being present on the control circuit.

P0948 vs. P0949

These codes concern very different transmission functions.

P0948 – Hydraulic Pump Relay/Control Circuit High

An electrical high condition has been detected in the hydraulic pump relay/control circuit.

P0949 – Auto Shift Adaptive Learning Not Completed

The transmission's adaptive-learning procedure has not successfully completed.

P0949 can occur after transmission or TCM work, while P0948 is primarily associated with the hydraulic pump control circuit.

If both codes are present, the hydraulic pressure system should be investigated carefully because inadequate pump operation could potentially interfere with transmission operation and adaptation.

How Serious Is P0948?

P0948 can be a serious transmission fault.

The reason is that hydraulic pressure is essential for many automatic transmission functions.

If the transmission depends on an electronically controlled pump and that pump cannot operate correctly, the vehicle may experience:

• Loss of hydraulic pressure

• Poor clutch engagement

• Gear-selection problems

• Slipping

• Limp mode

• Loss of Drive or Reverse

If the vehicle is still driving normally, it may be possible to move it carefully to a repair facility.

However, continued driving should be avoided if major transmission symptoms are present.

Can You Drive With P0948?

It depends on the symptoms and the transmission design.

If the vehicle shifts normally and there are no warning signs of pressure loss, a short drive to a repair facility may be possible.

However, stop driving and arrange further diagnosis if there is:

• Severe slipping

• Violent shifting

• Loss of Drive

• Loss of Reverse

• Transmission overheating

• Loud pump noise

• Limp mode

• Significant delay before engagement

Driving with inadequate hydraulic pressure can potentially cause further transmission damage.

How to Diagnose P0948

A proper diagnosis should determine why the pump-control circuit voltage or electrical condition is higher than expected.

1. Scan all control modules

Use a professional diagnostic scanner to check:

• TCM

• PCM

• Body-control module

• Transmission-related modules

Look for additional codes.

Other codes may identify the underlying electrical problem.

2. Check freeze-frame data

Review the conditions when P0948 was stored.

Useful information can include:

• Vehicle speed

• Engine RPM

• Transmission temperature

• Selected gear

• Pump command

• Pump status

• System voltage

3. Monitor live data

If supported by the vehicle, monitor:

• Hydraulic pump command

• Pump ON/OFF status

• Pump duty cycle

• Transmission pressure

• System voltage

• Transmission temperature

Compare the requested pump operation with its actual behavior.

4. Inspect the pump relay

If the vehicle uses a separate pump relay, check:

• Relay power supply

• Relay ground/control circuit

• Relay output

• Relay resistance

• Relay operation under load

A relay that appears to work during a basic continuity test may still fail under load.

5. Check the fuse and power supply

Inspect the relevant:

• Fuse

• Power feed

• Ground

• Power-distribution component

Do not replace a fuse repeatedly without determining why it failed.

6. Check for short to voltage

Because P0948 is a circuit-high code, inspect the control circuit for unwanted battery or ignition voltage.

Check the harness for:

• Melted insulation

• Chafing

• Pinched wires

• Incorrect repairs

• Contact with another powered wire

7. Inspect the pump connector

Check for:

• Corrosion

• Loose terminals

• Bent pins

• Water intrusion

• Damaged connector housing

• Poor terminal tension

8. Test the hydraulic pump

If the vehicle uses an electric pump, test:

• Power supply

• Ground

• Motor resistance where specified

• Current draw

• Pump activation

• Pump operation

Follow the manufacturer's test procedure because pump specifications vary.

9. Check hydraulic pressure

If the transmission design permits pressure testing, measure hydraulic pressure according to the manufacturer's procedure.

This can help determine whether the electrical problem is accompanied by an actual hydraulic-pressure problem.

10. Inspect transmission fluid

Check:

• Fluid level

• Fluid specification

• Fluid condition

• Leaks

• Contamination

• Metal debris where applicable

The correct fluid-level procedure should be followed because many transmissions require a specific temperature and procedure.

11. Check TCM output

If the relay, wiring, pump and power supply are all correct, verify whether the TCM is providing the correct control signal.

12. Evaluate the TCM last

A TCM fault is possible, but it should generally be considered only after the circuit has been thoroughly tested.

Replacing the TCM simply because P0948 is stored can lead to unnecessary expense.

Why P0948 Can Be Difficult to Diagnose

P0948 may be caused by either an electrical problem or a problem involving the pump itself.

The diagnostic challenge is determining whether:

The TCM is commanding the pump incorrectly

or

The pump/relay/circuit is producing an incorrect electrical response.

A basic visual inspection may not be enough.

The circuit may need to be tested:

• With the system powered

• Under load

• During pump activation

• At different operating temperatures

P0948 After Transmission Repair

If P0948 appeared after transmission repair or replacement, inspect any wiring and connectors disturbed during the work.

Pay particular attention to:

• Pump wiring

• Pump connector

• Relay

• Ground connections

• Transmission harness

• Power supply

A connector that was not fully seated can cause an electrical control fault immediately after repair.

P0948 After Transmission Replacement

After transmission replacement, verify that:

• The correct pump configuration is installed

• Electrical connectors are correct

• Wiring is routed correctly

• Grounds are properly connected

• Required programming has been completed

Some transmission systems may require module configuration after replacement.

P0948 After Battery Replacement

Battery replacement does not normally cause P0948 directly.

However, electrical problems can become apparent after battery work if:

• A connector was disturbed

• A power connection is loose

• Voltage was unstable

• A fuse or relay problem developed

Check the battery and charging system if the code appeared after electrical work.

Can P0948 Cause Limp Mode?

Yes.

If the transmission control system cannot reliably operate the hydraulic pump, it may activate a protective strategy.

Possible results include:

• Limp mode

• Limited gears

• Harsh shifting

• Delayed engagement

• Transmission warning light

• Reduced transmission functionality

The exact behavior depends on the transmission.

Can P0948 Damage the Transmission?

The code itself does not mechanically damage the transmission.

However, if P0948 results in inadequate hydraulic pump operation, the transmission may not receive the pressure required for proper clutch and gear operation.

Continued driving with:

• Slipping

• Low hydraulic pressure

• Delayed engagement

• Severe shifting

can potentially increase internal transmission wear.

This is why P0948 should not be ignored when transmission symptoms are present.

Common Diagnostic Mistakes With P0948

One common mistake is immediately replacing the hydraulic pump.

P0948 does not automatically mean the pump is defective.

The relay, wiring, connectors and control circuit must be tested first.

Another mistake is interpreting “Circuit High” as high transmission fluid pressure.

It refers to an electrical condition.

Another mistake is checking the pump only for continuity.

An electric pump can have acceptable resistance while still having an operating or load-related fault.

Another mistake is ignoring the power supply and ground.

The pump circuit should be evaluated as a complete electrical system.

What Is the Correct Repair for P0948?

The correct repair depends on the confirmed cause.

Possible repairs include:

• Replacing the hydraulic pump relay

• Repairing a short to voltage

• Repairing damaged wiring

• Repairing or replacing damaged connectors

• Replacing damaged terminals

• Correcting power-supply problems

• Repairing ground connections

• Replacing a faulty electric hydraulic pump

• Repairing the pump control module

• Updating or repairing TCM software when applicable

• Replacing the TCM when it is conclusively diagnosed as faulty

After the repair, the pump should be activated and tested to confirm that the electrical signal and hydraulic operation are within specification.

Final Thoughts on P0948

P0948 – Hydraulic Pump Relay/Control Circuit High indicates that the transmission control system has detected an electrical condition higher than expected in the hydraulic pump relay or control circuit.

The code does not automatically mean that the hydraulic pump has failed.

The most important diagnostic areas are the pump relay, wiring, connectors, power supply, grounds, pump motor and TCM control signal.

Because the hydraulic pump can be essential to transmission operation, P0948 can become a serious fault if it results in inadequate hydraulic pressure.

The correct diagnostic approach is to first determine whether the high electrical condition is caused by a short to voltage, relay problem, wiring fault, connector problem, pump electrical fault or control-module issue.

Only after these possibilities have been eliminated should expensive components such as the hydraulic pump or TCM be replaced.

P0948 should primarily be approached as an electrical hydraulic-pump control problem. A systematic electrical and hydraulic diagnosis can prevent unnecessary pump replacement and help avoid further transmission damage.