Fuel Pump Electrical Circuit Diagnosis. Geo Metro 1997

For 1990-2009 cars only

Makes 🢒 Geo 🢒 1997 🢒 Metro 🢒 Engine 🢒 Engine Controls - 1.3L 🢒 Fuel Pump Electrical Circuit Diagnosis

Schematic Reference: Engine Controls Schematics

Circuit Description

The powertrain control module (PCM) will energize the fuel pump relay for 2 seconds when the ignition switch is turned to the ON position. When the fuel pump relay is energized the fuel pump will operate and pressurize the fuel system. The fuel pump will continue to operate as long as the PCM is receiving ignition system reference pulses. The fuel pump will stop after 2 seconds if ignition system reference pulses are not detected.

Diagnostic Aids

Check for any of the following conditions:

•	Check the resistance of the fuel pump relay. The resistance across terminal 1 and terminal 2 is 79-95 ohms at 20°C (68°F). The resistance across terminal 3 and terminal 4 is infinite.

•	The fuel pump relay's electrical contacts may be pitted or sticking. Replace the fuel pump relay if tapping gently on the relay or wiggling the relay causes a change in the relay's operation.

•	The performance of the fuel pump relay may be affected by temperature. Check the fuel pump relay after sitting outside overnight and after running the engine 30 minutes.

Normal fuel pump electrical resistance is 0.8-1.5 ohms at 20°C (68°F).

An intermittent malfunction may be caused by a fault in the fuel pump relay electrical circuit. Inspect the wiring harness and components for any of the following conditions:

•	Backed out terminals.

•	Improper mating of terminals.

•	Broken electrical connector locks.

•	Improperly formed or damaged terminals.

•	Faulty terminal to wire connections.

•	Physical damage to the wiring harness.

•	Broken conductor inside the wire insulation.

•	Corrosion of electrical connections, splices, or terminals.

Use the following relay cavity table in order to locate the correct cavities to probe during diagnosis. The table layout corresponds to the cavity layout of the relay block.

Relay Cavity Identification
Switch Power
Switch Load
Coil Power	Coil Ground

Test Description

The numbers below refer to the step numbers in the diagnostic table.

The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

This step checks whether the fuel pump relay can operate the fuel pump. The PCM turns ON the fuel pump relay for 2 seconds when ever the ignition is cycled. Use a helper to operate the ignition switch while you listen for fuel pump operation or use a scan tool. The scan tool can be used to turn the fuel pump relay ON and OFF. The PCM will disable fuel pump relay control if any DTCs are set or if the fuel level is less than 20 percent.

This step checks the fuel pump relay control circuit.

This step checks for an electrical fault in the fuel tank or fuel pump wire harness.

The PCM will not turn ON the fuel pump relay while cranking the engine if there is no ignition reference pulses to the PCM. Check for a DTC P0335 and diagnose the DTC before replacing the PCM.

Step

Action

Values

Yes

Did you perform the Powertrain On-Board Diagnostic System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Remove the fuel filler cap.
Prepare to listen for fuel pump operation at the fuel filler pipe.
Turn ON the ignition, leaving the engine OFF.
Listen for fuel pump operation. Repeat the ignition cycle if necessary.

Does the fuel pump operate for approximately 2 seconds?

Go to Step 3

Go to Step 4

Disconnect the fuel pump relay.
Probe the fuel pump relay connector cavity 2 with a test lamp connected to B+. Refer to the Relay Cavity Identification table in Diagnostic Aids.

Does the test lamp illuminate while cranking the engine?

Go to Fuel System Diagnosis

Go to Step 19

Turn ON the ignition, leaving the engine OFF.
Disconnect the fuel pump relay.
With a test lamp connected to ground, probe the fuel pump relay connector cavity 4.

Did the test lamp illuminate?

Go to Step 5

Go to Step 9

Turn OFF the ignition.
Connect a fused jumper wire from the fuel pump relay connector cavity 3 to cavity 4.
Turn ON the ignition, leaving the engine OFF.
Listen for fuel pump operation. Repeat the ignition cycle if necessary.

Is the fuel pump ON?

Go to Step 12

Go to Step 6

Leave the fused jumper wire connected.
Remove the rear seat cushion. Refer to Seat Cushion Replacement - Rear in Seats.
Locate the fuel pump electrical connector C300 under the seat cushion.
Backprobe the fuel pump electrical connector ignition positive voltage circuit, PNK wire, with a test lamp connected to ground.

Does the test lamp illuminate?

Go to Step 7

Go to Step 10

Turn OFF the ignition.
Disconnect the fused jumper wire.
Disconnect the fuel pump electrical connector.
Probe the fuel pump electrical connector ground circuit, BLK wire (harness side), with a test lamp connected to B+.

Did the test lamp illuminate?

Go to Step 8

Go to Step 11

Remove the fuel tank. Refer to Fuel Tank Replacement .
Check for any of the following:

•	Check the fuel pump wiring harness for an open circuit from connector C300 to the fuel sender assembly.

•	Check for a fault in the fuel sender assembly electrical connector pass thru.

•	Remove the fuel sender assembly and check the fuel pump wire harness and electrical connections. Refer to Fuel Sender Assembly Replacement in Engine Controls.

Repair any faulty conditions found as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

Go to Step 20

Go to Step 18

Check for an open or a short in the WHT/BLU wire between the main relay and the fuel pump relay.
Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

Go to Step 20

Go to Main Relay Circuit Diagnosis

Repair the open or the short in the PNK wire between the fuel pump electrical connector C300 and the fuel pump relay. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 20

Repair the ground connection or the open in the fuel pump ground circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 20

Turn OFF the ignition.
Disconnect the fused jumper wire.
Turn ON the ignition, leaving the engine OFF.
Probe the fuel pump relay connector cavity 1 with a test lamp connected to ground.

Is the test lamp ON?

Go to Step 13

Go to Step 15

Probe the fuel pump relay connector cavity 2 with a test lamp connected to B+.

Is the test lamp ON while cranking the engine?

Go to Step 16

Go to Step 14

Backprobe the fuel pump relay control circuit at the PCM with a test lamp connected to B+.

Is test lamp ON while cranking the engine?

Go to Step 17

Go to Step 19

Repair the open or the short in the IG-COIL fuse circuit (BLK/WHT wire). Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 20

Replace the fuel pump relay. Refer to Fuel Pump Relay Replacement .

Is the action complete?

Go to Step 20

Repair the open in the fuel pump relay control circuit between the fuel pump relay and the PCM. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 20

Replace the fuel pump. Refer to Fuel Pump Replacement .

Is the action complete?

Go to Step 20

Replace the PCM. Refer to the Test Description and Powertrain Control Module Replacement .

Is the action complete?

Go to Step 20

Operate the vehicle within the conditions under which the original symptom was noted.

Does the system now operate properly?

System OK

Go to Diagnostic Aids