The high-pressure injection pump gets most of the attention, but it cannot manufacture fuel. Everything it does depends on a reliable supply coming from the tank, through the pickup, lines, filtration, water separation, and whatever transfer or lift pump the engine uses. When the supply falters, the sophisticated high-pressure system can look helpless—and the warning light may tell the story from the wrong end.
P008A: Low-Pressure Fuel Supply Too Low is an especially direct clue on engines equipped with that monitoring strategy. P008B points in the opposite direction, indicating excessive low-side pressure. Neither code tells you that the lift pump must be replaced. Clogged filters, a restricted pickup, air leakage on the suction side, inaccurate pressure sensing, control faults, and incorrect component installation can all influence the outcome. The type of transfer pump and whether the system operates under suction or positive pressure are application-dependent.
An electrical fault and a hydraulic fault are not the same thing
P0230–P0232, P0627–P0629, P062A, P025A–P025D, and P064A are associated with pump circuits, control modules, or performance monitoring. An open or shorted circuit may prevent a pump from running even when the pump itself is mechanically capable. A motor can also run while delivering inadequate flow under the engine’s actual demand. Listening for a pump to hum is therefore not a substitute for measuring the correct combination of pressure, volume, electrical supply, and commanded operation under specified conditions.
Fuel pump “A,” primary/secondary circuits, and fuel pump modules are naming conventions that must be translated through the specific wiring diagram. A scan tool that reports “fuel pump A” does not guarantee the vehicle uses two identically designed electric pumps. Some systems employ relays, some pulse-width-modulated controllers, and some engine designs generate their own supply pressure mechanically.
What fuel starvation looks like on the road
A weak supply may produce hard starts, low power on hills, hesitation under acceleration, or intermittent rail-pressure DTCs. The vehicle may idle beautifully and fail only when flow demand rises. It may recover after a short stop, leaving the driver certain the problem has vanished. That pattern is why a pressure reading taken only in the driveway can mislead; the supply system must be evaluated under conditions that make the complaint appear, with safe, manufacturer-approved test methods.
Contamination changes the equation. Water, gasoline, DEF, debris, or severe filter restriction can damage components or interfere with measurements. If metallic debris is found, replacing the transfer pump without determining the source and extent of contamination is unlikely to be a responsible fix. Fuel quality is part of the diagnosis, not an afterthought.
The diagnostic order that protects the expensive parts
A technician begins with supply voltage, grounds, fuses, connectors, filter condition, tank level, and evidence of restriction or aeration. Appropriate pressure and flow checks are then compared with specifications for the exact engine. Only after the supply side has been verified does it make sense to place heavy blame on the high-pressure system. The logic is simple: if the high-pressure pump is being starved at its inlet, measuring what happens at the rail cannot tell you how the pump would perform with a healthy supply.
Codes covered by this hub
| DTC or code family | What the fault describes | Diagnostic significance |
|---|---|---|
| P008A | Low-pressure fuel supply too low | Low-side supply fault where monitored; filter, pump, electrical control, restrictions, and air intrusion matter. |
| P0627 | Fuel pump A control circuit open | Open command/power circuit fault; exact pump A assignment is model-specific. |
| P0628 | Fuel pump A control circuit low | Low control circuit state requires electrical diagnosis. |
| P0629 | Fuel pump A control circuit high | High control circuit state requires electrical diagnosis. |
| P062A | Fuel pump A control circuit range/performance | Pump control response falls outside monitored performance expectations. |
| P025A | Fuel pump module control circuit open | Control-module command circuit open; distinguish controller, wiring and pump. |
| P025B | Fuel pump module control range/performance | Module feedback or command response outside expected behavior. |
| P025C | Fuel pump module control circuit low | Module control low state; electrical diagnosis required. |
| P025D | Fuel pump module control circuit high | Module control high state; electrical diagnosis required. |
| P0230 | Fuel pump primary circuit malfunction | Primary power/control circuit, not necessarily weak hydraulic delivery. |
| P0231 | Fuel pump secondary circuit low | Feedback or secondary circuit low; exact interpretation is application-dependent. |
| P0232 | Fuel pump secondary circuit high | Feedback or secondary circuit high; exact interpretation is application-dependent. |
| P008B | Low-pressure fuel supply too high | Excessive supply pressure; investigate return restrictions and control strategy. |
| P064A | Fuel pump control module fault | Pump controller malfunction indication; verify feed, ground, communications and load. |
Continue with P008A, P0087, and fuel quality problems. Our team can discuss which pump or injector tests make sense after the supply side is checked; send us the vehicle and code information to start a more useful conversation.
Keep exploring the right evidence
Codes guide a diagnosis but do not identify a failed pump or injector by themselves. Review nearby systems, compare the exact engine application, and seek qualified testing before deciding on a repair.