Error Code P0946 is defined as Hydraulic Pump Relay Circuit Range/Performance. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to the present. Of course, specifications on the definition, troubleshooting, and repairs vary from one make and model to another.

The job of the transmission pump is to turn the rotation force made by the engine into hydraulic pressure that runs the transmission and turns the wheels of the vehicle. If the hydraulic pump relay circuit is compromised or not running according to the parameters programmed by the Powertrain Control Module (PCM), then this code will be stored.

Common Symptoms

  • Harsh shifting patterns
  • Transmission slipping between gears
  • Unable to change gears

Possible Causes

  • Dirty or low transmission fluid
  • Damaged connectors or wirings
  • Defective hydraulic pump relay
  • Hydraulic pump relay open or shorted
  • Poor electrical connection at the hydraulic pump relay circuit
  • PCM or TCM problems

How to Check

Start the diagnosis by checking the quality and level of transmission fluid.

Also, test the hydraulic pump relay and make sure it is running properly.

Next, check the related wirings harness and connectors, and repair as needed. Also, look for any signs of damage in related components, such as bent, broken, pushed out, or corroded connector’s pin, particularly between the relay and the transmission.

Test the hydraulic pump relay/transmission pump relay.

How to Fix

  • Change of transmission fluid and filter
  • Repair or replacement of damaged connectors and wirings
  • Replacement of hydraulic pump relay
  • Reprogramming or replacement of PCM or TCM

Since this code refers to hydraulic or transmission pump relay problems, it should be considered serious, as the vehicle may not be working/running right. This results in drivability issues that may lead to severe and more expensive damages in the long run. Thus, it must be addressed as soon as possible.