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Home >> Cadillac >> 2006 >> Escalade EXT >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - 4.8L, 5.3L, And 6.0L - DTC P2121 To DTC U0107 >> DTC P2636 >> Test Description
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Test Description

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. The test lamp should illuminate as the primary fuel pump is commanded ON.
  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. If the test lamp illuminates, a short to ground is indicated.
  6. 9:  This step tests for a short to voltage on the control circuit of the secondary fuel pump relay. If the test lamp illuminates, a short to voltage is indicated.
  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
Connector End View Reference: Powertrain Control Module (PCM) Connector End Views or Engine Controls Connector End Views
1 Did you perform the Diagnostic System Check - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Vehicle
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. Probe the secondary fuel pump relay coil supply circuit with a test lamp connected to a good ground.
  5. Command the fuel pump relay ON with a scan tool.
Does the test lamp illuminate when the fuel pump relay is commanded ON?		 - Go to Step 3  Go to Step 22 
3 Probe the ignition voltage circuit of the secondary fuel pump relay, switch side, with a test lamp connected to a good ground.
Does the test lamp illuminate?		 - Go to Step 4  Go to Step 12 
4  Connect a 15-amp fused jumper wire between the ignition 1 voltage and secondary fuel pump supply voltage circuit of the secondary fuel pump relay harness connector.
Does the secondary fuel pump turn ON?		 - Go to Step 5  Go to Step 16 
5 
  1. Turn OFF the ignition.
  2. Remove the jumper wire from the secondary fuel pump relay harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the rear fuel level voltage parameter with a scan tool.
Is the rear fuel level sensor 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 wire between the ignition 1 voltage circuit and the secondary fuel pump supply voltage circuit of the secondary fuel pump relay harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the rear fuel level sensor voltage parameter with a scan tool.
Does the rear fuel level sensor 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 jumper wire from the secondary fuel pump relay harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the secondary fuel pump relay control circuit with a test lamp connected to B+.
Does the test lamp illuminate?		 - Go to Step 23  Go to Step 9 
9  Probe the secondary fuel pump relay control circuit 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. Jumper the following secondary fuel pump relay switch circuits from the secondary fuel pump relay to the secondary fuel pump relay harness connector:
    • The ignition 1 voltage circuit
    • The secondary fuel pump supply voltage circuit
  3. Jumper the secondary fuel pump relay coil supply circuit to B+.
  4. Turn ON the ignition, with the engine OFF.
  5. Jumper the control terminal of the secondary fuel pump relay to a good ground.
Does the secondary fuel pump turn ON when the fuel pump relay control terminal 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 .
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 .
Did you find and correct the condition?		 - Go to Step 31  Go to Step 14 
14 Test the voltage supply 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. Install a new fuse.
  3. Connect a 15-amp fused jumper wire between the ignition 1 voltage and the secondary fuel pump supply voltage circuit of the secondary fuel pump relay harness connector.
  4. Turn ON the ignition, with the engine OFF.
  5. Inspect the PCM 1 fuse.
Is the fuse open?		 - Go to Step 29  Go to Testing for Intermittent Conditions and Poor Connections
16
  1. Lower the rear fuel tank. Refer to Fuel Tank Replacement (Single Tank) or Fuel Tank Replacement (Dual Tanks - Front) or Fuel Tank Replacement (Dual Tanks - Rear) or Fuel Tank Replacement (Single Tank w/5.3L (L59) Engine) .
  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.
Does the test lamp illuminate?		 - 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 Test for an intermittent and for a poor connection at the harness connector of the secondary fuel pump relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 - Go to Step 31  Go to Step 28 
20 Test for an intermittent and for a poor connection at the harness connector of the secondary fuel pump. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 - Go to Step 31  Go to Step 29 
21 Test for an intermittent and for a poor connection at the harness connector of the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 - Go to Step 31  Go to Step 30 
22 Repair the open supply voltage circuit of the secondary fuel pump relay. Refer to Wiring Repairs .
Did you complete the repair?		 - Go to Step 31  -
23 Repair the short to ground in the control circuit of the secondary fuel pump relay. Refer to Wiring Repairs .
Did you complete the repair?		 - Go to Step 31  -
24 Repair the open ground circuit of the secondary fuel pump. Refer to Wiring Repairs .
Did you complete the repair?		 - Go to Step 31  -
25 Repair the open ignition voltage circuit of the secondary fuel pump relay. Refer to Wiring Repairs .
Did you complete the repair?		 - Go to Step 31  -
26 Repair the open supply voltage circuit of the secondary fuel pump. Refer to Wiring Repairs .
Did you complete the repair?		 - Go to Step 31  -
27 Repair the short to voltage on the control circuit of the secondary fuel pump relay. Refer to Wiring Repairs .
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 level sensor assembly. Refer to Fuel Sender Assembly Replacement (4.8L and 5.3L Engines) or Fuel Sender Assembly Replacement (5.3L (L59) Engine) or Fuel Sender Assembly Replacement (6.0L Engine - Dual Tanks - Front) or Fuel Sender Assembly Replacement (6.0L Engine - Dual Tanks - Rear) .
Did you complete the replacement?		 - Go to Step 31  -
30 Replace the PCM. Refer to Control Module References for replacement, setup, and programming.
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 have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List - Vehicle System OK
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