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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1069 (Engine Controls Diagnosis - 4.8L, 5.3L, & 6.0L (DTCS P2120 To U0107)) >> Diagnosis >> DTC P2636 >> Test Description

Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

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

  1. 2:  This step tests the supply voltage circuit of the secondary fuel pump relay.
  2. 4:  This step verifies the secondary fuel pump operation. Listen for an audible sound as the secondary fuel pump relay harness connector is jumpered.
  3. 5:  This step verifies that there is adequate fuel in the rear fuel tank. The rear fuel tank sensor voltage must be above 1 volt in order to continue.
  4. 7:  This step tests the secondary fuel pumps ability to transfer fuel. The rear fuel level sensor voltage should decrease while the secondary fuel pump is ON.
  5. 8:  This step tests for a short to ground on the control circuit of the secondary fuel pump relay.
  6. 9:  This step tests for a short to voltage on the control circuit of the secondary fuel pump relay.
  7. 10:  This step verifies the secondary fuel pump relay operation. An audible click should be heard as the secondary fuel pump relay control circuit is grounded. The secondary fuel pump should turn ON as the fuel pump relay control circuit is grounded.
DTC P2636

Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
1 Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
2 
IMPORTANT: The fuel level must be between 25-50 percent to perform this diagnostic procedure. If the fuel level is not within this range, misdiagnosis will occur.
  1. Turn OFF the ignition.
  2. Remove the secondary fuel pump relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the fuel pump supply voltage circuit of the secondary fuel pump relay and a good ground.
  5. Command the fuel pump ON with a scan tool.
Does the test lamp illuminate when the fuel pump is commanded ON?		 - Go to Step 3  Go to Step 22 
3 Probe the ignition 1 voltage circuit of the secondary fuel pump relay with a test lamp connected to a good ground.
Is the test lamp illuminated?		 - Go to Step 4  Go to Step 12 
4  Connect a 15-amp fused jumper wire between the ignition 1 voltage circuit of the secondary fuel pump relay and the fuel balance pump supply voltage circuit of the secondary fuel pump relay.
Does the secondary fuel pump turn ON?		 - Go to Step 5  Go to Step 16 
5 
  1. Turn OFF the ignition.
  2. Remove the 15-amp jumper wire from the secondary fuel pump relay circuits.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the fuel level sensor rear parameter with a scan tool.
Is the fuel level sensor rear voltage above the specified value?		 1 V Go to Step 7  Go to Step 6 
6 Add the specified amount of fuel to the fuel tank.
Did you complete the action?		 19 L (5 gal) Go to Step 7  -
7 
  1. Turn OFF the ignition.
  2. Connect a 15-amp fused jumper between the ignition 1 voltage circuit of the secondary fuel pump relay and the fuel balance pump supply voltage circuit of the secondary fuel pump relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the fuel level sensor rear parameter with a scan tool.
Does the fuel level sensor rear voltage decrease as the secondary fuel pump is operating?		 - Go to Step 8  Go to Step 18 
8 
  1. Turn OFF the ignition.
  2. Remove the 15-amp fused jumper wire from the secondary fuel pump relay circuits.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the secondary fuel pump relay control circuit of the secondary fuel pump relay with a test lamp that is connected to battery voltage.
Does the test lamp illuminate?		 - Go to Step 23  Go to Step 9 
9  Probe the secondary fuel pump relay control circuit of the secondary fuel pump relay with a test lamp connected to a good ground.
Does the test lamp illuminate?		 - Go to Step 27  Go to Step 10 
10 
  1. Turn OFF the ignition.
  2. Connect jumpers between the secondary fuel pump relay and the secondary fuel pump relay harness connector of the following circuits:
    • The ignition 1 voltage circuit
    • The secondary fuel pump sully voltage
  3. Connect a jumper between the secondary fuel pump relay coil supply circuit and the battery voltage.
  4. Turn ON the ignition, with the engine OFF.
  5. Connect a jumper between the control circuit terminal of the secondary fuel pump relay to a good ground.
Does the secondary fuel pump turn ON when the fuel pump relay control circuit jumper is grounded?		 - Go to Step 11  Go to Step 19 
11 Test the secondary fuel pump relay control circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 31  Go to Step 21 
12 Inspect the PCM 1 fuse.
Is the PCM 1 fuse open?		 - Go to Step 13  Go to Step 25 
13 Test the ignition 1 voltage circuit of the secondary fuel pump relay for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 31  Go to Step 14 
14 Test the fuel balance pump supply voltage circuit of the secondary fuel pump for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 31  Go to Step 15 
15
  1. Turn OFF the ignition.
  2. Replace the PCM 1 fuse.
  3. Connect a 15-amp fused jumper between the ignition 1 voltage circuit of the secondary fuel pump relay and the fuel balance pump supply voltage circuit of the secondary fuel pump relay.
  4. Turn ON the ignition, with the engine OFF.
Does the fuse in the jumper wire open?		 - Go to Step 29  Go to Intermittent Conditions
16
  1. Lower the rear fuel tank. Refer to Fuel Tank Replacement (Pickup) or Fuel Tank Replacement (Pickup - 5.3L (L59) Engine) or Fuel Tank Replacement (1500 Crew Cab) or Fuel Tank Replacement (Cab/Chassis - Front) or Fuel Tank Replacement (Cab/Chassis - Rear) .
  2. Disconnect the secondary fuel pump harness connector.
  3. Probe the voltage supply circuit of the secondary fuel pump with a test lamp connected to a good ground.
Is the test lamp illuminated?		 - Go to Step 17  Go to Step 26 
17 Probe the ground circuit of the secondary fuel pump with a test lamp connected to B+.
Does the test lamp illuminate?		 - Go to Step 20  Go to Step 24 
18 Inspect the fuel line between the primary and secondary fuel tanks for a restriction.
Did you find and correct the condition?		 - Go to Step 31  Go to Step 29 
19 Inspect for poor connections at the harness connector of the secondary fuel pump relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 31  Go to Step 28 
20 Inspect for poor connections at the harness connector of the secondary fuel pump. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 31  Go to Step 29 
21 Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 31  Go to Step 30 
22 Repair the open in the fuel pump supply voltage circuit. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 31  -
23 Repair the short to ground in the secondary fuel pump relay control circuit. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 31  -
24 Repair the open in the secondary fuel pump ground circuit. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 31  -
25 Repair the open ignition 1 voltage circuit of the secondary fuel pump relay. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 31  -
26 Repair the open in the fuel balance pump supply voltage circuit. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 31  -
27 Repair the short to voltage in the secondary fuel pump relay control circuit. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 31  -
28 Replace the secondary fuel pump relay.
Did you complete the replacement?		 - Go to Step 31  -
29 Replace the rear fuel sender assembly. Refer to Fuel Sender Assembly Replacement (4.8L, 5.3L, and 6.0L Engines) or Fuel Sender Assembly Replacement (5.3L (L59) Engine) .
Did you complete the replacement?		 - Go to Step 31  -
30 Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .
Did you complete the replacement?		 - Go to Step 31  -
31
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?		 - Go to Step 2  Go to Step 32 
32 Observe the Capture Info with a scan tool.
Are there any DTCs that are not diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List System OK
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