Error Code P0945 is defined as Hydraulic Pump Relay Circuit/Open. 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.

This error code is set when the Powertrain Control Module (PCM) has determined an electrical problem in the hydraulic pump relay circuit. The transmission pump is considered the most important transmission part in the gearbox.

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.

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 or wirings
  • Replacement of hydraulic pump relay
  • Reprogramming or replacement of PCM or TCM

Since the transmission pump creates the hydraulic pressure that turns the vehicle’s wheel, any problem with this component can cause drivability issues or render the vehicle inoperable. Thus, this code is considered serious.