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Home >> GMC >> 2001 >> C3500 HD 6.5 F, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - 6.5L - Troubleshooting >> Fuel Pump Electrical Circuit Diagnosis >> Test Description
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Test Description

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

  1. 2:  This step checks for proper operation of the fuel pump.
  2. 3:  This step checks the operation of the fuel pump by supplying 12 volts to the fuel pump control circuit.
  3. 5:  This step checks the battery feed circuit to the fuel pump relay.
Fuel Pump Electrical Circuit Diagnosis

Step Action Yes No
Schematic Reference:  Engine Controls Schematics 
1
IMPORTANT: Before clearing the DTCs, use the Scan Tool Capture Info in order to record the Freeze Frame/Failure Records for reference, as the data will be lost when the Clear Info function is used.
Did you perform the Diagnostic System Check-Engine Controls?		 Go to Step 2  Go to Diagnostic System Check - Engine Controls
2 
  1. Turn OFF the ignition for 10 seconds.
  2. Turn ON the ignition.
Does the fuel lift pump operate during the glow plug cycle?		 Go to Engine Cranks but Does Not Run  Go to Step 3 
3  Connect a 20-amp fused jumper wire between the battery voltage circuit of the fuel pump relay and the supply voltage circuit of the fuel pump.
Does the fuel pump operate?		 Go to Step 4  Go to Step 8 
4
  1. Disconnect the fuel pump relay.
  2. Turn ON the ignition, with the engine OFF.
  3. Probe the fuel pump relay battery feed terminal at the fuel pump relay harness connector with a test lamp to ground.
Does the test lamp illuminate?		 Go to Step 5  Go to Step 10 
5  Connect a test lamp between the fuel pump relay battery feed circuit harness connector and the fuel pump relay ground at the harness connector.
Does the test lamp illuminate?		 Go to Step 6  Go to Step 11 
6
  1. Connect a test lamp between the fuel pump relay control circuit and ground.
  2. Turn OFF the ignition for 20 seconds.
  3. Turn ON the ignition.
Does the test lamp turn ON during glow plug cycle and then turn OFF?		 Go to Step 7  Go to Step 12 
7
  1. Check for a poor connection at the fuel pump relay control connector terminal.
  2. If a problem is found, repair the problem as necessary.
Did you find and correct the condition?		 Go to Step 18  Go to Step 13 
8
  1. Disconnect the fuel pump harness connector at the fuel lift pump.
  2. Connect a 20-amp fused jumper to the fuel lift pump ignition 1 voltage circuit.
  3. Probe the fuel pump ignition 1 voltage circuit with a test lamp to ground.
Does the test lamp illuminate?		 Go to Step 9  Go to Step 15 
9 With a test lamp connected to battery positive, probe the fuel pump ground terminal, vehicle side, of the chassis harness fuel pump connector.
Does the test lamp illuminate?		 Go to Step 14  Go to Step 16 
10 Repair the open in the battery positive voltage circuit to the fuel pump relay harness connector terminal.
Did you complete the repair?		 Go to Step 18  -
11 Repair the open in the fuel pump relay ground circuit.
Did you complete the repair?		 Go to Step 18  -
12
  1. Check for an open or a short to ground in the harness between the fuel pump relay control connector terminal and the fuel pump relay control circuit.
  2. Check for a poor connection at the PCM fuel pump relay control circuit. Refer to Testing For Intermittent Conditions And Poor Connections or to Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 18  Go to Step 17 
13 Replace the fuel pump relay using the J 43244  Relay Puller Pliers. See Special Tools .
Did you complete the replacement?		 Go to Step 18  -
14 Replace the fuel lift pump. Refer to Fuel Pump Replacement .
Did you complete the replacement?		 Go to Step 18  -
15 Test the supply voltage circuit of the fuel pump for an open or high resistance between the fuel pump relay and the fuel pump. Refer to Testing For Intermittent Conditions And Poor Connections or to Wiring Repairs in Wiring Systems. Repair as necessary.
Did you complete the repair?		 Go to Step 18  -
16 Repair the open in the fuel pump harness ground circuit.
Did you complete the repair?		 Go to Step 18  -
17 Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .
Did you complete the replacement?		 Go to Step 18  -
18
  1. Use the scan tool in order to select DTC, Clear Info.
  2. Attempt to start the engine.
Does the engine start and continue to run?		 Go to Step 19  Go to Step 2 
19
  1. Allow the engine to idle until the normal operating temperature is reached.
  2. Select DTC, Failed This Ign.
Are there any DTCs displayed?		 Go to Diagnostic Trouble Code (DTC) List System OK
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