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 Descriptor

DTC P2636: Fuel Transfer Pump Flow Insufficient

### Circuit Description

The fuel tank on this vehicle is equipped with 2 fuel level sensors, one for each reservoir of the fuel tank. Fuel is transferred from the right side of the fuel tank to the left side of the fuel tank in order to ensure all of the usable fuel volume is available. The fuel pump supplies a small amount of pressurized fuel to the siphon jet pump through the fuel feed pipe. The pressurized fuel creates a venturi action inside the siphon jet pump. The venturi action causes the fuel to be drawn out of the right side of the fuel tank. Fuel is then transferred from the right side of fuel tank to the left side of fuel tank through the internal fuel transfer tube. This diagnostic tests for too large of a difference in fuel level between the left and right side of the fuel tank. The DTC sets if the control module determines that the left side fuel level is less than a predetermined amount of the right side fuel level.

The following table illustrates the difference between temperature, resistance, and voltage:

Fuel Level-Right or Left Sensor | Fuel Level Sensor Resistance | Fuel Level Sensor Voltage
--- | --- | ---
Empty | Low | Low
Full | High | High

### Conditions for Running the DTC

• | Before the engine control module (ECM) can report DTC P2636 failed, DTCs P0462, P0463, P2067, and P2068 must run and pass.

• | The ignition voltage is between 10-18 volts.

• | The engine speed is greater than 240 RPM.

• | DTC P2636 runs continuously when the above conditions exist for more than 4 minutes.

### Conditions for Setting the DTC

The ECM detects that the left side fuel level is less than 11 percent, and the right side fuel level is greater than 22 percent.

### Action Taken When the DTC Sets

DTC P2636 is a Type C DTC.

### Conditions for Clearing the MIL/DTC

DTC P2636 is a Type C DTC.

### Diagnostic Aids

Depending on the current fuel level, it may be difficult to locate a malfunctioning fuel level sensor. The condition may only occur when the fuel level is full or near empty. The fuel level sensor unit may need to be removed for further diagnosis. A fuel level sensor that has an intermittent condition causes this DTC to set.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Fuel System Description

#### 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

### Circuit/System Verification

1. Engine idling for 5 minutes, observe the DTC information with a scan tool. DTC P2636 should not set.
2. 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 harness connector of the left side fuel level sensor.
2. Ignition ON, verify the scan tool Fuel Level Sensor-Right (Secondary) Tank voltage parameter is at 5.0 V.

⇒ | If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM.

3. Install a 3 A fused jumper wire between the signal circuit terminal A and ground. Verify the scan tool Fuel Level Sensor-Right Tank voltage parameter is at 0.0 V.

⇒ | If greater than the specified range, test the signal circuit for a high resistance. If the circuit tests normal, replace the ECM.

4. Install a 3 A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal D. Verify the scan tool Fuel Level Sensor-Right Tank voltage parameter is at 0.0 V.

⇒ | If greater than the specified range, test the low reference circuit for a high resistance. If the circuit tests normal, replace the ECM.

5. Remove the fuel tank.
6. Remove the fuel tank primary and secondary modules and inspect for the following conditions:

• | A clogged secondary fuel strainer and pick up

• | A clogged or restricted siphon jet pump

• | Broken, clogged or restricted flex tubes, primary fuel tank module

• | Broken, clogged, disconnected, or restricted fuel transfer tube inside tank

⇒ | If you find any of the above conditions, repair as necessary.

7. If all circuits/connections test normal, test or replace the left/secondary fuel level sensor.

### Component Testing

1. Ignition OFF, remove the left fuel level sender from the fuel tank.
2. Connect a DMM between terminal A and terminal D.
3. Verify the secondary fuel level sender resistance remains within 40-250 Ω and changes smoothly while moving the float arm from stop to stop.

⇒ | If not within the specified range or changes erratically while moving the float arm from stop to stop, replace the fuel level sender.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Fuel Tank Draining

• | Fuel Tank Replacement

• | Primary Fuel Tank Module Replacement

• | Secondary Fuel Tank Module Replacement

• | Fuel System Cleaning

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