P0628 - Fuel Pump 'A' Control Circuit Low
System
Powertrain (Engine & Gearbox)
Technical Description
The control module has detected a fault in the Fuel Pump 'A' Control Circuit Low (P0628). The signal is below the lower threshold, typically from a short to ground or an internally shorted sensor.
Multimeter Test Points & Nominal Values
| Test Point / Component | Measurement | Nominal Target Range | Test Condition |
|---|---|---|---|
| Fuel Pump 'A' Control Circuit Low – Coil Resistance | Resistance (Ω) | 20 - 120 Ω (relay) / 8 - 40 Ω (solenoid) | Device disconnected at 20°C |
| Fuel Pump 'A' Control Circuit Low – Supply Voltage | Voltage (V) | 11.8 - 14.4 V | Ignition ON, high side of load |
| Fuel Pump 'A' Control Circuit Low – Control (Low Side) Rest / Active | Voltage (V) | Rest ≈ battery voltage / Active < 1.0 V | Module commanding device ON/OFF |
Device disconnected at 20°C
Ignition ON, high side of load
Module commanding device ON/OFF
Oscilloscope Waveform Analysis
5 ms/div, 50 V/divPossible Causes
Short to ground on the signal wire or an internal short circuit within Fuel Pump 'A' Control Circuit Low
Channel A:Verify dedicated wiring pins and signal pair for circuit A against the schematic.
Chafed or pinched wiring harness along the signal path to Fuel Pump 'A' Control Circuit Low
Internal mechanical wear or carbon deposits inside Fuel Pump 'A' Control Circuit Low
Defective internal output driver or reference circuit in the control module for Fuel Pump 'A' Control Circuit Low
Symptoms
4
Recommended Solution
Compare signal voltage and resistance between circuit A and companion circuit B at module connector.
Measure signal wire resistance to chassis ground with connector unplugged (must exceed 10 kΩ; low reading confirms short to ground).
Verify loaded supply voltage and harness terminal pins at Fuel Pump 'A' Control Circuit Low.
Check circuit continuity and ground-side voltage drop (< 0.05 V) for Fuel Pump 'A' Control Circuit Low.
Command device via scan-tool bidirectional control to verify mechanical operation and flyback spike.
Mechanic's Tip
When an inductive relay/solenoid turns off, an inductive flyback spike (60 - 300 V) MUST appear on the scope. Absence of the spike indicates an open coil winding or an open module driver.