Fault code P0946 – hydraulic pump relay circuit range/performance

Fault code P0946 is called “Hydraulic Pump Relay Circuit Range/Performance” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0946

This Diagnostic Trouble Code (DTC) is a generic code. Error P0946 is considered a generic code as it applies to all makes and models of vehicles. It is set when the control module (PCM) detects a low signal in the hydraulic pump relay circuit.

Fault code P0946 – hydraulic pump relay circuit range/performance

Hydraulic pumps are designed for pumping fluids, and in automobiles they are often used in the lubrication system. The lubricating liquid is pumped under a certain pressure to the moving parts and mechanisms.

The pump is regulated by a signal coming from the module (PCM) to the pump control relay. The fluid is then routed to the various hydraulic circuits with the appropriate pressure.

Code P0946 is set by the PCM when the hydraulic pump relay is not working properly due to a mismatch in the circuit performance range. The Malfunction Indicator Light (MIL) is then illuminated on the instrument panel.

Symptoms of vehicle malfunctions

The main signal that an error P0946 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. Check engine control lamp on the control panel will light up (the code will be recorded in the memory as a fault).
  2. Detonation in the engine.
  3. Increased engine noise, there may also be ringing and rattling.
  4. Overheating of the engine.
  5. Oil leakage.
  6. Increased fuel consumption.
  7. Decreased engine power.
  8. Symptoms similar to ignition failure may be present.

Fault code P0946 is serious, because the cause of this error may affect the hydraulic pressure. The increase or decrease of which directly affects the operational safety.

Factors that can cause this error code

The error code P0946 can mean that one or more of the following problems have occurred:

  • Pressure control relay is defective.
  • Defective hydraulic pump.
  • Contaminated fluid or clogged oil filter.
  • Low oil level in engine.
  • Channels for passing engine oil are clogged.
  • Other mechanical problems inside engine.
  • Wiring problem or damaged connector.
  • Sometimes faulty PCM module is the cause.

How to fix or reset OBD-2 code P0946

Some suggested steps for troubleshooting and fix the error code P0946:

  1. Change engine oil and filter.
  2. Fill oil to the required level.
  3. Flushing to clean internal engine channels.
  4. Test, if necessary replace defective pressure control relay.
  5. Repair or replace faulty hydraulic pump.
  6. Check connectors as well as wiring.
  7. Flash or replace PCM.

Diagnose and repair of problems

Before you begin the process of troubleshooting P0946, you should research the Technical Service Bulletins (TSBs) for your specific vehicle. In some cases, this can save you a lot of time by pointing you in the right direction.

Next, you should check the oil level and check for contamination. Before you change the engine oil, you should check the vehicle’s records to see when the filter and fluid were last changed.

After that, you should do a detailed visual inspection to check the condition of the wiring for obvious defects. Check the connectors and wiring to the hydraulic pump control relay and PCM.

This error is often caused by oil leaking through the oil pump solenoid valve wiring. The oil getting on the contacts causes a short circuit and as a consequence of this fault.

Normal readings for wiring and connections should be 0 ohms of resistance. The wiring continuity check should always be done with the power disconnected from the circuit. To avoid short-circuiting and creating additional damage.

Resistance or lack of continuity indicates faulty wiring that is open or shorted. In this case, repair or replacement will be required to clear code P0946.

On which vehicles does this problem occur most frequently

Fault code P0946 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • BMW
  • Buick
  • Cadillac
  • Chevrolet
  • Citroen
  • Honda
  • Mercedes-Benz (W164, W211)

Fault code P0946 can sometimes be found with other errors. The most common are the following: P0945, P0947, P0948.

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