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P0629 OBD-II Trouble Code: Fuel Pump "A" Control Circuit High

check engine light

P0629 code definition

When the vehicle’s PCM stores the P0629 code, it means that there is an issue with the “A” control circuit in the fuel pump.

What the P0629 code means

Either the vehicle’s PCM, or another supporting control module, has found a problem with the fuel pump’s “A” control circuit. The supporting control modules include, but are not limited to:

  • Body control module
  • Fuel injection control module
  • Alternative fuel control module
  • Turbo control module
  • Anti-lock brake control module
  • Anti-theft module
  • Traction control module
  • Cruise control module
  • Instrument panel control module
  • Climate control module
  • Proximity alert module

What causes the P0629 code?

If the fuel pump “A” control circuit is faulty, the P0629 code is stored. This often means that the malfunction is in a certain area of the system, as opposed to any one component or circuit. Usually, the P0629 code is caused by a defective fuel pump, or a problem with the fuel pump relay. Other causes include:

  • Bad connectors, or shorted or open wiring in the CAN bus harness
  • A loose ground strap in the control module
  • A broken ground wire in the control module
  • A defective CAN bus

What are the symptoms of the P0629 code?

Symptoms of the P0629 code can include: * The code being stored

If the Check Engine Light does not come on right away, the code may be pending.

How does a mechanic diagnose the P0629 code?

The mechanic will focus on the CAN (controller area network) bus. This is what allows the various microcontrollers in the vehicle to communicate independent of a host computer. These microcontrollers regulate practically all of the vehicle’s electrical functions, and the PCM is the master controller.

It is possible for individual controllers to fail, but not common. So first, the mechanic will test each individual module, and replace as needed. The process starts with using an OBD-II scanner, and continues with several (but not necessarily all) of the following:

  • Visually checking connectors and wiring
  • Replacing any damaged wires, connectors and components
  • Re-testing the system
  • If all appears to be working properly, recording the codes and freeze frame data, and then clearing out the codes
  • Running the vehicle to see if the codes come back (if they don’t come back immediately, the problem could be intermittent and more difficult to diagnose)
  • Using a special scanner like Tech II or Autohex to identify the general area in which the problem is occurring
  • Disconnecting and testing all the CAN bus pins (this could be costly)
  • Testing control module ground circuits with battery ground
  • Identifying ground discrepancies using an auxiliary ground cable
  • Checking for corroded or loose connectors that could be increasing circuit resistance
  • Using a digital volt ohmmeter to test individual controller connector continuity, using a CAN bus wiring diagram and pin out value chart
  • Comparing findings with the manufacturer’s specs, and repairing shorted or open circuits as needed

Common mistakes when diagnosing the P0629 code

Repairs are sometimes unsuccessful if the communication failure is misdiagnosed. This is because the wrong component has been identified, and unnecessarily replaced.

How serious is the P0629 code?

This is not a life-threatening issue, but if not corrected, it could lead to more serious problems down the road. You do not have to get the problem fixed immediately, but should have it dealt with in order to avoid more expensive repairs later on.

What repairs can fix the P069 Code?

A mechanic can fix or replace damaged wiring and corroded connectors, and replace any defective modules.

Additional comments for consideration regarding the P0629 code

This type of problem often takes a long time to diagnose, and the wiring harnesses that need to be evaluated and/or repaired are very complex. Often, it is more cost-effective to simply replace any wiring that is suspect.

Need help with a P0629 code?

At YourMechanic, it will be our pleasure to send a mobile mechanic to your home or place of work. We will be glad to provide you with a free quote as well. To arrange an appointment, call us 1-800-701-6230, or use our convenient online form.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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