A P0628 code in your 2023 Volvo XC90 indicates that the ECM has detected low voltage in the fuel pump control circuit. Unlike the open circuit indicated by P0627, P0628 suggests the circuit is shorted to ground or has excessive current draw that pulls voltage below normal levels.
Low Voltage Circuit Analysis
When the fuel pump control circuit experiences a short to ground, the pathway offers less resistance than intended. Current flows to ground rather than through the relay coil, and voltage at measurement points drops abnormally low. The ECM detects this condition and stores P0628.
Common Causes
A short to ground in the control wiring is the primary cause. This can occur from chafed insulation touching metal components, water intrusion creating ground paths, or damaged connectors. An internally shorted relay coil draws excessive current and creates low readings. In some cases, the ECM's fuel pump driver circuit fails in a low or shorted condition.
Symptoms in Your XC90
Fuel pump operation may be inconsistent or prevented entirely if the short is severe enough. The check engine light illuminates. Blown fuses in the control circuit may occur if overcurrent protection exists. Starting problems develop as fuel delivery becomes unreliable.
Volvo-Specific Diagnostics
Using Volvo VIDA or dealer-level diagnostics, monitor fuel pump control circuit status. Check for short circuits in the wiring between the CEM (Central Electronic Module) and fuel pump relay. Measure control circuit resistance with components disconnected—it should be infinite to ground. Inspect the fuel pump relay for internal damage and the harness for physical damage.