P0629 — Fuel Pump “A” Control Circuit High #

Note: The wording of this code may vary depending on vehicle manufacturer.

• Fuel Pump “A” Control Circuit High (General, OBD-II Standard)
• Fuel Pump Relay Control Circuit High (Ford, GM)
• Fuel Pump Primary Circuit High Input (Chrysler)
• Fuel Pump Control Module Circuit High (Volkswagen/Audi)

Summary of DTC P0629 #

DTC P0629 sets when the engine control module (ECM) or powertrain control module (PCM) detects a high electrical signal in the fuel pump “A” control circuit. This circuit is responsible for regulating power delivery to the fuel pump, an electric device that delivers fuel from the tank to the engine. A “circuit high” condition means the voltage is higher than expected—often indicating a wiring issue, relay failure, or module fault. This code may result in starting issues or even cause the engine to stall, depending on the severity of the problem. Early diagnosis is critical to avoid being stranded or damaging the fuel system.

Common Symptoms for DTC P0629 #

When P0629 is stored, the vehicle may exhibit a range of symptoms—some obvious, others more subtle. Typically, drivers may notice difficulty starting the engine or an intermittent loss of power. In certain cases, the check engine light illuminates with no discernible drivability issues. If left unchecked, this fault can escalate from a nuisance to a serious reliability concern.

• Check Engine Light (CEL) illuminated
• Engine cranks but will not start
• Intermittent engine stalling
• Loss of power under load
• Longer-than-normal engine cranking time
• Possible no fuel pump noise when key is ON

Likely Causes for P0629 (In Order of Frequency) #

The P0629 code is typically triggered by electrical faults or component failures within the fuel pump control circuit. The most common root causes are related to wiring, relays, and sometimes the control module itself. In rare cases, internal faults within the fuel pump can also cause this code.

1. Faulty fuel pump relay — The relay may be stuck closed or have melted contacts.
2. Shorted wiring or connectors — Damaged, corroded, or pinched wires can cause high voltage readings.
3. Defective fuel pump control module — Some vehicles use a dedicated module to manage the pump.
4. Failed fuel pump (internal short) — Though less common, the pump itself can create a high voltage circuit fault.
5. PCM/ECM malfunction — Rare, but a faulty control unit can misinterpret signals.

Step-by-Step Diagnostic for P0629 #

A careful, methodical approach is essential to pinpoint the exact cause of P0629. Electrical issues can be elusive—like finding a loose thread in a tightly woven fabric. Follow these steps to efficiently isolate the fault:

1. Verify the code — Use a scan tool to confirm P0629 is present and check for related codes (e.g., P0627, P0628).
2. Inspect fuel pump fuse and relay — Check the relay for sticking, corrosion, or burn marks. Replace if suspect.
3. Check wiring and connectors — Look for visible damage, corrosion, or loose connections from the relay to the fuel pump and ECM/PCM.
4. Test circuit voltage — With the key ON, use a digital multimeter to check for correct voltage at the fuel pump connector and relay output.
5. Bypass relay (if applicable) — Safely bypass the relay to see if the fuel pump operates. If yes, the relay is likely faulty.
6. Check control module operation — If all wiring and relays check out, test the fuel pump control module (if equipped) or substitute with a known good unit.
7. Test the fuel pump — As a last step, bench-test the fuel pump for internal shorts or resistance outside specifications.

Possible Repairs for DTC P0629 #

Repairing P0629 depends entirely on the underlying cause. Always address wiring faults and relay issues before replacing costly components. Here’s a breakdown of typical repairs, aligned with the most common causes.

• Replace faulty fuel pump relay — Swap in a new relay if the old one is burnt, stuck, or otherwise defective.
• Repair or replace damaged wiring/connectors — Cut out corroded wires, solder in new sections, and clean or replace connectors as needed.
• Replace fuel pump control module — If diagnosed as faulty, install a new OEM module and reprogram if required by the manufacturer.
• Replace fuel pump assembly — Only if the pump is internally shorted or fails resistance tests.
• Repair or reprogram PCM/ECM — Rare, but sometimes necessary after all other options are exhausted.

Is It Safe to Drive with P0629? #

Limited/no: It is generally not safe to continue driving with P0629. This code indicates a fault in your vehicle’s fuel delivery system—if the pump fails or the circuit becomes completely open, the engine may stall unexpectedly. This poses a safety risk, especially at high speeds or in traffic. At best, you may experience poor performance or occasional no-starts; at worst, you could be left stranded. Immediate diagnosis and repair are strongly advised.

Vehicles Most Affected by P0629 #

While P0629 is a generic OBD-II code and can appear on virtually any modern vehicle, it is more frequently reported on certain makes and models, particularly those with complex fuel pump control circuits or modules. Based on field experience, these vehicles see higher than average occurrence:

• Ford F-Series (2011–2019)
• Chevrolet Silverado/GMC Sierra (2014–2020)
• Chrysler/Dodge/Jeep with TIPM (2007–2016)
• Volkswagen Jetta/Passat (2009–2018)
• Audi A4/A6 (2010–2017)

Common Mistakes & Best Practices with P0629 #

A rushed diagnosis of P0629 can lead to unnecessary part replacements and wasted time. Avoid these pitfalls and follow proven diagnostic strategies to save money and headaches.

• Mistaking a blown fuse for the root cause — Fuses rarely blow without an underlying problem. Always find the source of the overload.
• Replacing the fuel pump prematurely — In most cases, relays and wiring are more likely to fail than the pump itself.
• Ignoring intermittent wiring faults — Flexing harnesses and connectors during diagnosis can reveal hidden shorts or opens.
• Not verifying repairs — Always clear the code and perform a complete road test to ensure the issue is resolved.

Quick FAQ on P0629 #

Got questions? Here are quick answers to what drivers and techs ask most about P0629:

• Q: Can a weak battery cause P0629?
  A: Not directly. While low voltage can cause other fuel system codes, P0629 specifically refers to a high voltage or shorted circuit.
• Q: Do I need to replace the fuel pump if I see P0629?
  A: Not necessarily. Most often, relays or wiring are at fault. Test all related components before considering pump replacement.
• Q: Will clearing the code fix the problem?
  A: No. The code will return unless the underlying electrical issue is resolved.