For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC P0628 00: Fuel Pump Relay Control Circuit Low Voltage
DTC P0629 00: Fuel Pump Relay Control Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Battery Voltage - Relay Switch | 1 | 2 | -- | --
Fuel Pump Supply Voltage | 1 | 2 | 3 | --
Fuel Pump Relay Control | P0628 00 | P0629 00 | P0629 00 | --
Fuel Pump Relay Ground | -- | -- | -- | --
Fuel Pump Ground | -- | 2 | -- | --
1. The fuel pump fuse opens and the engine cranks but does not run. 2. The engine cranks but does not run. 3. The fuel pump operates continuously and the battery will discharge.

### Circuit/System Description

The engine control module (ECM) provides ignition voltage to the coil side of the fuel pump relay whenever the engine is cranking or running. The ECM enables the fuel pump relay as long as the engine is cranking or running, and ignition system reference pulses are received. If no ignition system reference pulses are received, the ECM turns OFF the fuel pump. The fuel pump relay control circuit is equipped with a feedback circuit that is pulled up to 2.5 V within the ECM. The ECM can determine if the control circuit is open, shorted to ground, or shorted to a voltage by monitoring the feedback voltage.

### Conditions for Running the DTC

• | The engine speed is greater than 80 RPM.

• | The ignition voltage is 10-18 V.

• | The ECM has commanded the fuel pump relay ON and OFF at least once during the ignition cycle.

• | The above conditions are met for less than 1 s.

• | DTCs P0628 00 or P0629 00 runs continuously once the above conditions are met.

### Conditions for Setting the DTC

#### P0627 00

The ECM detects the voltage on the fuel pump relay control circuit is within a predetermined range when the control circuit is commanded OFF. The condition exists for greater than 4 s, or a cumulative of 30 s.

#### P0628 00

The ECM detects the fuel pump relay control circuit voltage is less than 2.21 V when the control circuit is commanded ON. The condition exists for greater than 4 s, or a cumulative of 30 s.

#### P0629 00

The ECM detects the fuel pump relay control circuit voltage is greater than 2.21 V when the control circuit is commanded OFF. The condition exists for greater than 4 s, or a cumulative of 30 s.

### Action Taken When the DTC Sets

DTCs P0628 00 and P0629 00 are Type B DTCs.

### Conditions for Clearing the DTC

DTCs P0628 00 and P0629 00 are Type B DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

#### Special Tools

EL-43244 Relay Puller Pliers

For equivalent regional tools, refer to Special Tools.

### Circuit/System Verification

1. Ignition ON, command the fuel pump relay ON and OFF with a scan tool. You should hear an audible click.
2. Attempt to start the engine. Observe the DTC information with a scan tool. DTC P0628 00, or P0629 00 should not set.
3. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the freeze frame/failure records data.

### Circuit/System Testing

1. Ignition OFF, disconnect the KR23A Fuel Pump Relay with the EL-43244 Relay Puller Pliers .
2. Connect a test lamp between the control circuit terminal 85 of the KR23A Fuel Pump Relay and ground.
3. Ignition ON, command the KR23A Fuel Pump Relay ON and OFF with a scan tool. The test lamp should turn ON and OFF as commanded.

⇒ | If the test lamp remains OFF all the time, test for a short to ground or an open/high resistance on the control circuit. If circuit/connections test normal, replace the K20 Engine Control Module (ECM).

⇒ | If the test lamp remains ON all the time, test for a short to voltage on the KR23A Fuel Pump Relay control circuit. If circuit/connections test normal, replace the K20 Engine Control Module (ECM).

4. Ignition OFF, connect a test lamp between the KR23A Fuel Pump Relay control circuit terminal 85 and the ground circuit terminal 86 of the KR23A Fuel Pump Relay.
5. Ignition ON, command the fuel pump ON and OFF with a scan tool. The test lamp should turn ON and OFF as commanded.

⇒ | If the test lamp does not turn ON when commanded, repair the open/high resistance in ground circuit terminal 86 of the KR23A Fuel Pump Relay.

6. If all circuits/connections test normal, test or replace the KR23A Fuel Pump Relay.

### Component Testing

#### Static Test

1. Test for 70-110 Ω between terminals 85 and 86 of the KR23A Fuel Pump Relay.

⇒ | If not within the specified range, replace the KR23A Fuel Pump Relay.

2. Test for infinite resistance between the following terminals of the KR23A Fuel Pump Relay:

• | 30 and 86

• | 30 and 87

• | 30 and 85

• | 85 and 87

⇒ | If continuity is detected, replace the KR23A Fuel Pump Relay.

3. Connect a 20A fused jumper wire from the positive terminal of the battery to KR23A Fuel Pump Relay terminal 85. Connect a jumper wire from the negative terminal of the battery to KR23A Fuel Pump Relay terminal 86. Test for less than 2 Ω between terminals 30 and 87 of the KR23A Fuel Pump Relay.

⇒ | If greater than the specified range, replace the KR23A Fuel Pump Relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Relay Replacement

• | Control Module References for engine control module replacement, setup, and programming