P0947 Hydraulic Pump Relay Circuit Low

The P0947 trouble code is an OBD-II diagnostic trouble code related to the electrical circuit that controls a transmission's hydraulic pump relay.

P0947 – Hydraulic Pump Relay Circuit Low

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

In simple terms, the transmission computer is detecting an abnormally low electrical condition in the circuit used to control the transmission's hydraulic pump.

Depending on the vehicle, this circuit may involve:

• Hydraulic pump relay

• Electric transmission pump

• Fuse

• Wiring harness

• Power supply

• Ground

• Connectors

• Pump control circuit

• TCM

Importantly, P0947 does not automatically mean that the hydraulic pump itself has failed.

What Does P0947 Mean?

P0947 – Hydraulic Pump Relay Circuit Low

Automatic transmissions require hydraulic pressure to operate many internal components.

Hydraulic pressure can be used to control:

• Clutch packs

• Brakes

• Valve bodies

• Shift mechanisms

• Pressure-control systems

• Gear engagement

In transmissions equipped with an electronically controlled hydraulic pump, the TCM must be able to control the pump reliably.

A simplified system can be represented as:

TCM → Pump relay/control circuit → Hydraulic pump → Hydraulic pressure → Transmission operation

When the control module detects that the electrical signal in the pump relay circuit is below the expected level, it can store P0947.

What Does “Circuit Low” Mean?

The word “Low” refers to the electrical signal, not necessarily low transmission hydraulic pressure.

P0947 does not directly mean:

• Low transmission fluid

• Low transmission fluid pressure

• Low engine RPM

• Low transmission temperature

It means the control module has detected an electrical voltage or signal below its expected value.

A low electrical signal can be caused by:

• Short to ground

• Open or high-resistance circuit

• Faulty relay

• Weak power supply

• Poor ground

• Damaged wiring

• Corroded connector

• Pump electrical fault

• Control-module problem

The exact cause depends on the vehicle's circuit design.

What Is the Hydraulic Pump Relay?

A relay is an electrically controlled switch.

It allows the control module to operate a component that may require more electrical current than the control module can safely supply directly.

A simplified relay circuit can be viewed as:

TCM control → Relay → Hydraulic pump power

When the TCM requests hydraulic pump operation, the relay switches the pump's power circuit.

If the relay circuit develops an abnormal low signal, the TCM may store P0947.

Does P0947 Mean the Hydraulic Pump Is Bad?

Not necessarily.

This is an important distinction.

P0947 identifies a problem with the hydraulic pump relay circuit, not necessarily a mechanical or electrical failure of the pump itself.

Possible causes include:

• Faulty relay

• Blown fuse

• Poor power supply

• Short to ground

• Broken wire

• High-resistance connection

• Corroded connector

• Poor ground

• Faulty pump motor

• TCM control problem

The complete circuit should be tested before replacing the pump.

Symptoms of P0947

Symptoms vary depending on the transmission design and severity of the fault.

Possible symptoms include:

• Check Engine Light

• Transmission warning light

• Harsh shifting

• Delayed engagement

• Delayed Drive engagement

• Delayed Reverse engagement

• Transmission slipping

• Limited gear operation

• Limp mode

• Hydraulic pump not operating

• Pump-related noise

• Transmission overheating

• Vehicle refusing to move

Some vehicles may continue to operate normally for a limited period, particularly if another hydraulic pressure source or backup operating strategy is available.

Common Causes of P0947

Faulty hydraulic pump relay

The relay itself may fail internally.

Possible problems include:

• Burned contacts

• Stuck contacts

• Internal open circuit

• Incorrect switching

• Coil failure

• Excessive contact resistance

A relay should be tested according to the manufacturer's procedure rather than replaced automatically.

Blown fuse

If the hydraulic pump is powered through a dedicated fuse, a blown fuse can prevent proper relay or pump operation.

The reason the fuse failed should also be investigated.

Repeatedly replacing a blown fuse without finding the underlying fault is not a proper repair.

Short to ground

A short to ground can pull the control signal or power circuit below its expected voltage.

Possible causes include:

• Damaged insulation

• Chafed wiring

• Pinched harness

• Wire touching the transmission housing

• Incorrect previous repair

Broken or high-resistance wiring

A partially broken wire may not be completely open.

Instead, it may create excessive resistance.

This can result in:

• Voltage drop

• Weak pump operation

• Relay malfunction

• Low circuit readings

Corroded connector

Corrosion can increase resistance or interrupt the circuit.

Inspect:

• Pump connector

• Relay connector

• TCM connector

• Ground connections

• Power-distribution connections

Poor ground

A weak ground connection can prevent the relay or pump from operating correctly.

Check:

• Ground straps

• Ground terminals

• Chassis grounds

• Transmission grounds

Faulty electric hydraulic pump

If the vehicle uses an electric hydraulic pump, an internal pump problem can affect the circuit.

Possible faults include:

• Motor winding failure

• Internal short

• Excessive current draw

• Internal connector damage

• Pump controller failure

The pump should be electrically tested before replacement.

Power supply problem

A weak battery or charging-system problem can cause electrical abnormalities.

Check:

• Battery condition

• Charging voltage

• Main power connections

• Relevant fuses

• Power-distribution system

TCM control problem

The TCM may have a problem controlling the relay.

However, the TCM should generally be considered only after the external circuit has been tested.

Can Low Transmission Fluid Cause P0947?

Low transmission fluid does not normally cause P0947 directly.

However, low fluid can cause serious hydraulic problems, including:

• Pump cavitation

• Low hydraulic pressure

• Slipping

• Delayed engagement

• Noise

• Transmission overheating

These symptoms may occur at the same time as an electrical pump-control fault.

The fluid level should therefore be checked, but low fluid should not be assumed to be the direct cause of a circuit-low electrical code.

Can Dirty Transmission Fluid Cause P0947?

Dirty or contaminated fluid can affect:

• Pump operation

• Valve-body operation

• Hydraulic pressure

• Solenoid operation

• Clutch engagement

However, dirty fluid does not normally cause the electrical relay circuit to become low.

If P0947 is present, both the electrical system and the hydraulic system should be evaluated when necessary.

P0947 vs. P0948

These two codes identify opposite electrical conditions.

P0947 – Hydraulic Pump Relay 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.

With P0947, particular attention should be given to:

• Short-to-ground conditions

• Open circuits

• High resistance

• Weak power supply

• Poor grounds

• Relay faults

P0947 vs. P0949

These codes concern completely different aspects of transmission operation.

P0947 – Hydraulic Pump Relay Circuit Low

An electrical low condition exists in the hydraulic pump relay circuit.

P0948 – Hydraulic Pump Relay/Control Circuit High

An electrical high condition exists in the pump relay/control circuit.

P0949 – Auto Shift Adaptive Learning Not Completed

The transmission adaptive-learning process has not been successfully completed.

If P0947 and P0949 appear together, the pump-control problem should be investigated first because insufficient or unstable hydraulic operation could prevent successful transmission adaptation.

How Serious Is P0947?

P0947 can be a serious transmission fault.

The severity depends on how the hydraulic pump and relay are used by the particular transmission.

If the pump is essential for generating hydraulic pressure and it cannot operate correctly, the transmission may experience:

• Loss of hydraulic pressure

• Poor clutch engagement

• Slipping

• Harsh shifting

• Loss of gears

• Limp mode

• Loss of Drive or Reverse

If these symptoms are present, continued driving can potentially cause further transmission damage.

Can You Drive With P0947?

If the vehicle is shifting normally and there are no signs of hydraulic-pressure loss, a short drive to a repair facility may be possible.

However, caution is recommended.

Do not continue driving if there is:

• Severe transmission slipping

• Violent shifting

• Loss of Drive

• Loss of Reverse

• Significant engagement delay

• Loud pump noise

• Transmission overheating

• Limp mode

A transmission operating without sufficient hydraulic pressure can suffer additional damage.

How to Diagnose P0947

A proper diagnosis should determine why the electrical signal in the hydraulic pump relay circuit is lower than expected.

1. Scan all control modules

Use a professional diagnostic scanner to check:

• TCM

• PCM

• Body-control module

• Transmission-related modules

Record all stored and pending codes.

Related codes can provide valuable clues.

2. Check freeze-frame data

Review the conditions under which P0947 was stored.

Useful information may include:

• Vehicle speed

• Engine RPM

• Transmission temperature

• Selected gear

• System voltage

• Pump command

• Pump status

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 commanded pump operation with actual system behavior.

4. Inspect the hydraulic pump relay

Check the relay for:

• Correct power supply

• Correct ground/control signal

• Correct output voltage

• Coil resistance

• Contact resistance

• Proper switching

A relay can pass a basic continuity test and still fail under load.

5. Check the fuse

Inspect the pump-related fuse.

If it is blown, determine why before installing another fuse.

Possible causes include:

• Short circuit

• Pump motor failure

• Wiring damage

• Excessive current draw

6. Check battery and charging voltage

Verify:

• Battery condition

• Charging-system output

• Voltage stability

• Main grounds

• TCM power supply

Low system voltage can create misleading transmission electrical faults.

7. Check for a short to ground

Because P0947 is a circuit-low code, inspect the circuit for unintended contact with ground.

Look for:

• Chafed wires

• Pinched wires

• Melted insulation

• Harness damage

• Incorrect repairs

8. Check voltage drop

Voltage-drop testing can identify high-resistance connections that a basic continuity test may miss.

Test:

• Power side

• Ground side

• Relay contacts

• Pump power supply

• Pump ground

9. Inspect connectors

Check for:

• Corrosion

• Bent pins

• Loose terminals

• Backed-out terminals

• Water intrusion

• Poor terminal tension

10. Test the hydraulic pump

If the transmission uses an electric hydraulic pump, test:

• Power

• Ground

• Motor resistance where specified

• Current draw

• Activation

• Pump operation

Follow the manufacturer's specifications.

11. Check hydraulic pressure

If applicable, measure transmission hydraulic pressure according to the manufacturer's procedure.

This helps determine whether the electrical fault is also causing an actual hydraulic-pressure problem.

12. Inspect transmission fluid

Check:

• Fluid level

• Correct fluid specification

• Fluid condition

• Leaks

• Contamination

• Metal debris where applicable

The correct temperature and procedure should be used when checking fluid level.

13. Check TCM control

If the relay, wiring, power supply, grounds and pump all test correctly, verify that the TCM is producing the correct control signal.

14. Evaluate the TCM last

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

Why P0947 Can Be Difficult to Diagnose

A circuit-low code does not always mean that a wire is completely grounded.

The problem can also be caused by voltage drop or excessive resistance.

For example, a corroded connector may still pass some electrical current, but the voltage reaching the relay or pump may be too low.

This is why proper voltage-drop testing is often more useful than simply checking continuity.

P0947 After Transmission Repair

If P0947 appeared immediately after transmission repair, inspect the components and wiring disturbed during the repair.

Pay particular attention to:

• Pump wiring

• Pump connector

• Relay

• Fuse

• Ground connections

• Transmission harness

A connector that is partially seated can create a circuit-low condition.

P0947 After Transmission Replacement

After transmission replacement, verify:

• Correct electrical connectors

• Correct wiring

• Proper grounds

• Correct pump configuration

• Correct fuse and relay

• Proper module programming where required

The wiring harness should also be checked for pinching or damage caused during installation.

P0947 After Battery Replacement

Battery replacement does not normally cause P0947 directly.

However, if the code appeared immediately afterward, check:

• Battery terminals

• Main grounds

• Power connections

• Relevant fuses

• Charging voltage

A loose battery or ground connection can cause multiple electrical faults.

Can P0947 Cause Limp Mode?

Yes, it can.

If the transmission control system detects that it cannot reliably control 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 response depends on the vehicle.

Can P0947 Damage the Transmission?

P0947 itself does not mechanically damage the transmission.

The potential danger comes from the condition causing the code.

If the hydraulic pump cannot generate sufficient pressure, the transmission may experience:

• Clutch slipping

• Incomplete clutch engagement

• Abnormal shifting

• Excessive heat

• Increased internal wear

Continued driving under these conditions can potentially turn an electrical problem into a more expensive mechanical transmission problem.

Common Diagnostic Mistakes With P0947

One common mistake is immediately replacing the hydraulic pump.

P0947 does not automatically mean that the pump has failed.

The relay, fuse, power supply, ground, wiring and connectors should be tested first.

Another mistake is interpreting “Circuit Low” as low transmission fluid pressure.

The code refers to an electrical circuit condition.

Another common mistake is replacing the relay without checking why the relay circuit became abnormal.

If a pump motor is drawing excessive current or a wire is shorted, the replacement relay may fail again.

Another mistake is performing only a continuity test.

A circuit can have continuity and still suffer from excessive resistance or voltage drop.

What Is the Correct Repair for P0947?

The correct repair depends on the confirmed cause.

Possible repairs include:

• Replacing the hydraulic pump relay

• Replacing a blown fuse after correcting the underlying fault

• Repairing a short to ground

• Repairing damaged wiring

• Repairing high-resistance connections

• Replacing damaged terminals

• Repairing or replacing connectors

• Repairing ground connections

• Correcting power-supply problems

• Replacing a faulty electric hydraulic pump

• Repairing the pump control circuit

• Updating or repairing TCM software where applicable

• Replacing the TCM when it is conclusively diagnosed as faulty

After the repair, the pump should be activated and tested to verify both electrical operation and hydraulic performance.

Final Thoughts on P0947

P0947 – Hydraulic Pump Relay Circuit Low indicates that the transmission control system has detected an electrical signal or voltage lower than expected in the hydraulic pump relay circuit.

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

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

Because the hydraulic pump can be essential to transmission operation, P0947 can become a serious problem if the electrical fault prevents the transmission from generating or maintaining adequate hydraulic pressure.

The correct diagnostic approach is to first determine whether the low electrical condition is caused by a short to ground, open circuit, high resistance, weak power supply, poor ground, faulty relay, connector problem or pump electrical fault.

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

P0947 should primarily be approached as an electrical hydraulic-pump relay circuit problem. A systematic voltage, resistance and voltage-drop diagnosis can prevent unnecessary component replacement and help protect the transmission from secondary damage.