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Severity: Moderate Code type: Generic (all makes)

P0629 Code: Fuel Pump "A" Control Circuit High

Battery voltage is leaking into the fuel pump control line – a short, corrosion bridge or add-on wiring.

At a glance

Severity: 3/5 – Moderate3/5

Severity: Moderate

Meaning
Fuel Pump "A" Control Circuit High
System
ECU & Outputs · Powertrain
Safe to drive?
With caution
Typical repair cost
$20–$1,600
DIY difficulty
Moderate

P0629 means the PCM measured more voltage on its fuel pump control output than the commanded state allows, or saw excessive current when it tried to switch the output on – either way, the control line is connected to a power source it shouldn't be. On the common low-side design the PCM grounds the relay coil; if that wire is also touching a 12-volt circuit, the driver sees a dead short when it switches on, protects itself and turns off, so the pump never runs and the engine won't start. On designs where the PCM supplies the coil, a short to power can keep the relay energized even with the key off, running the pump and draining the battery. Corrosion bridges in relay sockets and aftermarket anti-theft or remote-start wiring spliced into this wire are classic sources.

Can I keep driving? If the car starts and runs normally, drive it to a shop soon. If the pump can be heard running with the key off or the battery keeps going flat, disconnect the battery or pull the pump fuse until it's repaired – a continuously running pump is a fire risk after a collision.

How to read P0629

How to read P0629P10263294
  1. P Powertrain
  2. 0 Generic (SAE)
  3. 6 Computer & outputs
  4. 29 Specific fault

Symptoms

  • Crank-no-start because the PCM shuts its fuel pump driver off
  • Intermittent stalling, sometimes when switching on lights or wipers that share a harness
  • Fuel pump running with the key off on some designs, with a battery that goes flat overnight
  • Fuel pump relay clicking rapidly or buzzing
  • Problem started after an alarm, remote start or tracking device was installed

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Control wire chafed against a battery-powered wire in the same harness 26%
  2. Corrosion bridging the relay socket's power terminal to the control terminal 20%
  3. Aftermarket remote start, alarm or kill-switch wiring spliced into the control line 18%
  4. Relay with a shorted coil causing driver overcurrent 14%
  5. Internal fault in the fuel pump driver module back-feeding voltage 12%
  6. PCM driver or its monitoring circuit failed 10%

Diagnosis step by step

Diagnostic flow: P06291Check freeze frame and circuitstatus2Look for voltage that shouldn't bethere3Find the source by pulling fuses4Inspect the relay socket closely5Trace any aftermarket wiring6Measure coil current and driverresponse

  1. Check freeze frame and circuit status

    Note whether the code set with the key on, while cranking or while driving, and whether it set once or repeatedly. Many PCMs show a status such as 'short to battery' for this output, which confirms the fault type before you start measuring.

    Tools: OBD-II scanner

  2. Look for voltage that shouldn't be there

    Remove the relay, unplug the PCM connector and measure the control wire to ground with the key off, then with the key on. It must read 0 V in both cases. Any voltage means the wire is picking up power from another circuit.

    Tools: Multimeter

  3. Find the source by pulling fuses

    With the meter still connected and showing voltage, pull fuses one at a time. The fuse whose removal makes the voltage disappear identifies the circuit the control wire is shorted to, which tells you which harness section to open up.

    Tools: Multimeter, Pliers

  4. Inspect the relay socket closely

    Relay sockets that have seen water often grow a green or white corrosion bridge between the high-current terminal and the coil terminals. Clean it out, check for melted plastic and replace the socket terminals if they're damaged.

    Tools: Flashlight, Screwdriver

  5. Trace any aftermarket wiring

    Look under the dash and near the steering column for add-on modules with splices into a wire that runs to the fuel pump relay. Remove or correctly re-wire them and retest; a poorly done fuel-kill circuit easily feeds voltage into the control line.

    Tools: Flashlight

  6. Measure coil current and driver response

    Put an ammeter in series with the relay coil: a healthy coil draws roughly 0.1–0.2 A. Much more means shorted turns overloading the PCM driver. With wiring and relay proven good, a code that sets instantly points to the pump driver module or the PCM.

    Tools: Multimeter

Where the parts are

Charging system and control modules – P06291234567
Charging system and control modules
  1. 1Battery
  2. 2Alternator
  3. 3Engine computer (ECM)
  4. 4CAN bus
  5. 5Transmission
  6. 6Wheel speed sensor
  7. 7High-voltage battery

Repair options & costs

RepairDIY?Estimated cost
Clean or replace corroded relay socket terminals Yes $60–$200
Replace relay Yes $20–$80
Repair wire shorted to power No $120–$400
Remove or rewire aftermarket device No $100–$300
Replace fuel pump driver module or PCM No $200–$1,600

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Emissions / smog test impact

Will fail

P0629 turns on the check engine light, which is an automatic fail at an OBD emissions inspection. Once the short is repaired, clear the code and drive normally until the monitors report ready.

Frequently asked questions

Why won't the engine start if the circuit is 'high'?

On most vehicles the PCM turns the pump on by grounding the relay coil. If the wire is also connected to 12 volts, switching it to ground creates a short, and the PCM protects itself by shutting the output off – so the relay never clicks and the pump never runs.

Could my remote starter cause P0629?

Yes. Remote start and anti-theft systems often interrupt or tap the fuel pump relay control wire. A splice in the wrong place or a module that back-feeds voltage produces exactly this code. Disconnecting the add-on is a quick test.

Is it safe to pull the fuel pump fuse to stop a battery drain?

Yes, as a temporary measure it's the right move if the pump runs with the key off; the car won't start until the fuse is back in. Get the short found soon rather than living with a pulled fuse.

How is P0629 different from P0232?

P0629 concerns the low-current control wire from the PCM to the relay or module. P0232 is about voltage on the heavy feed wire to the pump itself. Different wire, different test points, although a stuck relay can occasionally set both.

Sources