Code
P0629
Generic
P — Powertrain
Fuel Pump A Control Circuit High
Views:
UK: 19
EN: 31
RU: 29
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on the fuel pump A control circuit
- Stuck or welded fuel pump relay contacts
- Faulty fuel pump module (internal electronics) feeding the control circuit
- Corroded, damaged or disconnected wiring or connector
- Failed PCM/ECM driver transistor or internal short
- Aftermarket wiring or accessories tied into the fuel pump circuit
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Fuel pump may run continuously or fail to be commanded off
- Hard start, no start or intermittent stalling
- Parasitic battery drain when vehicle is off
- Reduced or erratic fuel pressure/delivery
- Possible buzzing/relay chatter at relay box
What to check
- Confirm DTC P0629 and note freeze-frame/conditions
- Visual inspection of fuel pump relay, fuse, connectors and wiring for damage or corrosion
- Check for aftermarket splices or bypass wiring to pump
- Measure battery voltage and check for parasitic draw with key off
- Backprobe the fuel pump control circuit at the relay and at the PCM connector
- Swap relay with identical known-good relay (if applicable) and re-check
Signal parameters
- Typical: control is a low-side switch (PCM grounds the relay coil). When commanded ON: control pin ~0–1 V (grounded). When OFF: control pin floats/high (near battery through relay coil).
- Fault condition: control voltage higher than expected when PCM commands low (example: > ~5 V or near battery voltage while commanded ON).
- For modules with PWM control: expected duty 0–100% at manufacturer-specific frequency (often tens to hundreds of Hz); waveform should switch between near 0 V and near battery.
- Nominal battery voltage: ~12.0–14.5 V with engine running — compare measured values to this.
Diagnostic algorithm
- Verify the code with a scanner and record freeze-frame data and ignition/state when the fault set.
- Visually inspect harnesses, relay box, pump module connector and ground points for corrosion, melted insulation, or aftermarket taps.
- With key ON (engine off), backprobe the PCM pump-control pin and measure voltage while commanding the pump (some tools can request/activate the pump). Observe whether the PCM attempts to pull the circuit low.
- If control circuit reads high when PCM should be pulling it low, isolate whether the high is coming from the relay or the pump module: unplug the fuel pump connector or relay coil circuit and re-test the control pin.
- If unplugging the pump/relay makes the control voltage return to expected values, inspect/replace the pump module or repair wiring to the module. If the control remains high with loads disconnected, suspect a relay short to +B or PCM fault.
- Swap the fuel pump relay with an identical known-good relay (if accessible) and retest to rule out a stuck relay.
- Perform continuity and short-to-battery checks on the control wire between the PCM, relay and pump module. Repair any shorted/short-to-B wires or poor connector terminals.
- Use a lab scope to check waveform under commanded ON: confirm PWM characteristics if applicable and look for battery feedback or irregular switching.
- Only after all wiring, relay and pump module checks fail should the PCM be considered for replacement — confirm PCM driver failure with bench or manufacturer procedures.
- After repairs, clear codes, verify no reoccurrence and perform a functional test (operate pump, check fuel pressure, verify key-off current draw).
Likely causes
- Short to constant battery +B on control wire (most common)
- Relay contacts stuck closed or relay coil wiring shorted
- Damaged connector (pin pushed out, corrosion) at pump module or relay
- Failed pump module with internal driver feeding back voltage
- PCM output stage failure (less common)
Fault status
Status
PCM detected abnormally high voltage on Fuel Pump A control circuit. Possible short to battery, stuck relay, defective pump module or PCM driver fault. Circuit requires wiring/relay/pump/PCM investigation.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
P0629
HUMMER
P — Powertrain
Fuel Pump Relay Control Circuit High Voltage
Views:
UK: 6
EN: 11
RU: 9
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on the fuel pump A control circuit
- Stuck or welded fuel pump relay contacts
- Faulty fuel pump module (internal electronics) feeding the control circuit
- Corroded, damaged or disconnected wiring or connector
- Failed PCM/ECM driver transistor or internal short
- Aftermarket wiring or accessories tied into the fuel pump circuit
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Fuel pump may run continuously or fail to be commanded off
- Hard start, no start or intermittent stalling
- Parasitic battery drain when vehicle is off
- Reduced or erratic fuel pressure/delivery
- Possible buzzing/relay chatter at relay box
What to check
- Confirm DTC P0629 and note freeze-frame/conditions
- Visual inspection of fuel pump relay, fuse, connectors and wiring for damage or corrosion
- Check for aftermarket splices or bypass wiring to pump
- Measure battery voltage and check for parasitic draw with key off
- Backprobe the fuel pump control circuit at the relay and at the PCM connector
- Swap relay with identical known-good relay (if applicable) and re-check
Signal parameters
- Typical: control is a low-side switch (PCM grounds the relay coil). When commanded ON: control pin ~0–1 V (grounded). When OFF: control pin floats/high (near battery through relay coil).
- Fault condition: control voltage higher than expected when PCM commands low (example: > ~5 V or near battery voltage while commanded ON).
- For modules with PWM control: expected duty 0–100% at manufacturer-specific frequency (often tens to hundreds of Hz); waveform should switch between near 0 V and near battery.
- Nominal battery voltage: ~12.0–14.5 V with engine running — compare measured values to this.
Diagnostic algorithm
- Verify the code with a scanner and record freeze-frame data and ignition/state when the fault set.
- Visually inspect harnesses, relay box, pump module connector and ground points for corrosion, melted insulation, or aftermarket taps.
- With key ON (engine off), backprobe the PCM pump-control pin and measure voltage while commanding the pump (some tools can request/activate the pump). Observe whether the PCM attempts to pull the circuit low.
- If control circuit reads high when PCM should be pulling it low, isolate whether the high is coming from the relay or the pump module: unplug the fuel pump connector or relay coil circuit and re-test the control pin.
- If unplugging the pump/relay makes the control voltage return to expected values, inspect/replace the pump module or repair wiring to the module. If the control remains high with loads disconnected, suspect a relay short to +B or PCM fault.
- Swap the fuel pump relay with an identical known-good relay (if accessible) and retest to rule out a stuck relay.
- Perform continuity and short-to-battery checks on the control wire between the PCM, relay and pump module. Repair any shorted/short-to-B wires or poor connector terminals.
- Use a lab scope to check waveform under commanded ON: confirm PWM characteristics if applicable and look for battery feedback or irregular switching.
- Only after all wiring, relay and pump module checks fail should the PCM be considered for replacement — confirm PCM driver failure with bench or manufacturer procedures.
- After repairs, clear codes, verify no reoccurrence and perform a functional test (operate pump, check fuel pressure, verify key-off current draw).
Likely causes
- Short to constant battery +B on control wire (most common)
- Relay contacts stuck closed or relay coil wiring shorted
- Damaged connector (pin pushed out, corrosion) at pump module or relay
- Failed pump module with internal driver feeding back voltage
- PCM output stage failure (less common)
Fault status
Status
PCM detected abnormally high voltage on Fuel Pump A control circuit. Possible short to battery, stuck relay, defective pump module or PCM driver fault. Circuit requires wiring/relay/pump/PCM investigation.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
P0629
LAND ROVER
P — Powertrain
Fuel Pump A Control - High Circuit
Views:
UK: 4
EN: 7
RU: 7
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on the fuel pump A control circuit
- Stuck or welded fuel pump relay contacts
- Faulty fuel pump module (internal electronics) feeding the control circuit
- Corroded, damaged or disconnected wiring or connector
- Failed PCM/ECM driver transistor or internal short
- Aftermarket wiring or accessories tied into the fuel pump circuit
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Fuel pump may run continuously or fail to be commanded off
- Hard start, no start or intermittent stalling
- Parasitic battery drain when vehicle is off
- Reduced or erratic fuel pressure/delivery
- Possible buzzing/relay chatter at relay box
What to check
- Confirm DTC P0629 and note freeze-frame/conditions
- Visual inspection of fuel pump relay, fuse, connectors and wiring for damage or corrosion
- Check for aftermarket splices or bypass wiring to pump
- Measure battery voltage and check for parasitic draw with key off
- Backprobe the fuel pump control circuit at the relay and at the PCM connector
- Swap relay with identical known-good relay (if applicable) and re-check
Signal parameters
- Typical: control is a low-side switch (PCM grounds the relay coil). When commanded ON: control pin ~0–1 V (grounded). When OFF: control pin floats/high (near battery through relay coil).
- Fault condition: control voltage higher than expected when PCM commands low (example: > ~5 V or near battery voltage while commanded ON).
- For modules with PWM control: expected duty 0–100% at manufacturer-specific frequency (often tens to hundreds of Hz); waveform should switch between near 0 V and near battery.
- Nominal battery voltage: ~12.0–14.5 V with engine running — compare measured values to this.
Diagnostic algorithm
- Verify the code with a scanner and record freeze-frame data and ignition/state when the fault set.
- Visually inspect harnesses, relay box, pump module connector and ground points for corrosion, melted insulation, or aftermarket taps.
- With key ON (engine off), backprobe the PCM pump-control pin and measure voltage while commanding the pump (some tools can request/activate the pump). Observe whether the PCM attempts to pull the circuit low.
- If control circuit reads high when PCM should be pulling it low, isolate whether the high is coming from the relay or the pump module: unplug the fuel pump connector or relay coil circuit and re-test the control pin.
- If unplugging the pump/relay makes the control voltage return to expected values, inspect/replace the pump module or repair wiring to the module. If the control remains high with loads disconnected, suspect a relay short to +B or PCM fault.
- Swap the fuel pump relay with an identical known-good relay (if accessible) and retest to rule out a stuck relay.
- Perform continuity and short-to-battery checks on the control wire between the PCM, relay and pump module. Repair any shorted/short-to-B wires or poor connector terminals.
- Use a lab scope to check waveform under commanded ON: confirm PWM characteristics if applicable and look for battery feedback or irregular switching.
- Only after all wiring, relay and pump module checks fail should the PCM be considered for replacement — confirm PCM driver failure with bench or manufacturer procedures.
- After repairs, clear codes, verify no reoccurrence and perform a functional test (operate pump, check fuel pressure, verify key-off current draw).
Likely causes
- Short to constant battery +B on control wire (most common)
- Relay contacts stuck closed or relay coil wiring shorted
- Damaged connector (pin pushed out, corrosion) at pump module or relay
- Failed pump module with internal driver feeding back voltage
- PCM output stage failure (less common)
Fault status
Status
PCM detected abnormally high voltage on Fuel Pump A control circuit. Possible short to battery, stuck relay, defective pump module or PCM driver fault. Circuit requires wiring/relay/pump/PCM investigation.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
P0629
MITSUBISHI
P — Powertrain
Suction control valve high
Views:
UK: 5
EN: 10
RU: 11
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on the fuel pump A control circuit
- Stuck or welded fuel pump relay contacts
- Faulty fuel pump module (internal electronics) feeding the control circuit
- Corroded, damaged or disconnected wiring or connector
- Failed PCM/ECM driver transistor or internal short
- Aftermarket wiring or accessories tied into the fuel pump circuit
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Fuel pump may run continuously or fail to be commanded off
- Hard start, no start or intermittent stalling
- Parasitic battery drain when vehicle is off
- Reduced or erratic fuel pressure/delivery
- Possible buzzing/relay chatter at relay box
What to check
- Confirm DTC P0629 and note freeze-frame/conditions
- Visual inspection of fuel pump relay, fuse, connectors and wiring for damage or corrosion
- Check for aftermarket splices or bypass wiring to pump
- Measure battery voltage and check for parasitic draw with key off
- Backprobe the fuel pump control circuit at the relay and at the PCM connector
- Swap relay with identical known-good relay (if applicable) and re-check
Signal parameters
- Typical: control is a low-side switch (PCM grounds the relay coil). When commanded ON: control pin ~0–1 V (grounded). When OFF: control pin floats/high (near battery through relay coil).
- Fault condition: control voltage higher than expected when PCM commands low (example: > ~5 V or near battery voltage while commanded ON).
- For modules with PWM control: expected duty 0–100% at manufacturer-specific frequency (often tens to hundreds of Hz); waveform should switch between near 0 V and near battery.
- Nominal battery voltage: ~12.0–14.5 V with engine running — compare measured values to this.
Diagnostic algorithm
- Verify the code with a scanner and record freeze-frame data and ignition/state when the fault set.
- Visually inspect harnesses, relay box, pump module connector and ground points for corrosion, melted insulation, or aftermarket taps.
- With key ON (engine off), backprobe the PCM pump-control pin and measure voltage while commanding the pump (some tools can request/activate the pump). Observe whether the PCM attempts to pull the circuit low.
- If control circuit reads high when PCM should be pulling it low, isolate whether the high is coming from the relay or the pump module: unplug the fuel pump connector or relay coil circuit and re-test the control pin.
- If unplugging the pump/relay makes the control voltage return to expected values, inspect/replace the pump module or repair wiring to the module. If the control remains high with loads disconnected, suspect a relay short to +B or PCM fault.
- Swap the fuel pump relay with an identical known-good relay (if accessible) and retest to rule out a stuck relay.
- Perform continuity and short-to-battery checks on the control wire between the PCM, relay and pump module. Repair any shorted/short-to-B wires or poor connector terminals.
- Use a lab scope to check waveform under commanded ON: confirm PWM characteristics if applicable and look for battery feedback or irregular switching.
- Only after all wiring, relay and pump module checks fail should the PCM be considered for replacement — confirm PCM driver failure with bench or manufacturer procedures.
- After repairs, clear codes, verify no reoccurrence and perform a functional test (operate pump, check fuel pressure, verify key-off current draw).
Likely causes
- Short to constant battery +B on control wire (most common)
- Relay contacts stuck closed or relay coil wiring shorted
- Damaged connector (pin pushed out, corrosion) at pump module or relay
- Failed pump module with internal driver feeding back voltage
- PCM output stage failure (less common)
Fault status
Status
PCM detected abnormally high voltage on Fuel Pump A control circuit. Possible short to battery, stuck relay, defective pump module or PCM driver fault. Circuit requires wiring/relay/pump/PCM investigation.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
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