Code
P0628
HUMMER
P — Powertrain
Fuel Pump Relay Control Circuit Low Voltage
Views:
UK: 23
EN: 55
RU: 42
AI status
Completed
Completed
100%
Causes
- Poor battery or low system voltage
- Blown or corroded fuse or faulty fuel pump relay
- Damaged, corroded, or loose wiring/connectors in the relay control circuit
- Short to ground or high resistance in the relay control wire
- Faulty fuel pump relay coil
- Faulty PCM or internal PCM driver (less common)
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- No-start or hard-start condition
- Intermittent or no fuel pump operation; low fuel pressure
- Engine stalls shortly after start
- Possible cranking with no fuel delivery
What to check
- Read and record freeze frame / live data and confirm P0628 is current
- Verify battery voltage (should be ~12.4–12.8V with key off, ~13.5–14.8V when running)
- Inspect fuel pump relay, fuse(s), and associated fuse holder for corrosion or damage
- Visually inspect wiring and connectors at the relay, fuel pump, and PCM for corrosion, damage, or loose pins
- Check for other related codes (fuel pump circuit codes)
Signal parameters
- Relay feed terminal (battery side) expected: near battery voltage (~12V) with key ON
- PCM control terminal expected when RELAY OFF: high (open or ~12V) depending on circuit; when PCM commands ON: control should be pulled low (~0–0.5 V) if PCM grounds the coil
- Typical fault threshold: control circuit voltage significantly below expected when it should be high (example: below ~4–5V)
- Relay coil continuity normally: measurable ohms (varies by relay, typically 50–200 Ω)
Diagnostic algorithm
- Confirm code, review freeze frame and monitor fuel pump relay control voltage with a scan tool/ DMM while key ON and during cranking
- Verify battery voltage and main power/grounds to relay and PCM; charge or replace battery if low
- Inspect fuses and relay; swap with known-good relay of same type if available
- Back-probe relay coil terminals: one side should see battery voltage, the control side should change between near battery voltage and near ground when PCM commands fuel pump ON. Note voltages and compare to expected
- If control side is low when it should be high, inspect wiring for short to ground between relay and PCM; repair damaged insulation or connectors
- If control side is open/high when it should be low (PCM should ground), check for open circuit between PCM and relay; wiggle-test harness and repair connectors/pins
- Remove relay and check coil resistance; replace relay if coil open or out of spec
- If wiring and relay check good, test fuel pump by applying bench power to confirm pump operation
- If all wiring, relay, and pump are OK, test or substitute PCM (follow vehicle manufacturer procedures) — only replace PCM after verifying network and programming requirements
Likely causes
- Corroded/loose connector at fuel pump relay or PCM
- Relay control wire shorted to ground or damaged insulation
- Weak battery or poor main power/ground at fuse/relay feed
- Faulty fuel pump relay coil or relay contacts
- PCM output transistor or driver degraded
Fault status
Status
PCM has detected a low-voltage condition on the fuel pump relay control circuit. This indicates the control line voltage is lower than expected and may prevent proper relay operation and fuel delivery.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
HTML Workshop Manuals AI manual library for HUMMER Click to show available manuals 77
HUMMER 2010 H3 Alpha
HTML ManualHUMMER 2010 H3 Base, Standard
HTML ManualHUMMER 2010 H3 Base, Automatic
HTML ManualHUMMER 2010 H3T Alpha
HTML ManualHUMMER 2010 H3T Base, Standard
HTML ManualHUMMER 2010 H3T Base, Automatic
HTML ManualHUMMER 2009 H2 4D Utility Wagon
HTML ManualHUMMER 2009 H2 4D Utility Pickup
HTML ManualYour experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email