GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2000 🢒 Chevy C Silverado - 2WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 DTC P1172 Sec Fuel Pump Insufficient/No Fuel Flow

Circuit Description

The Secondary fuel pump is located in the rear fuel tank. The secondary fuel pump is powered by a secondary fuel pump relay which is seperate from the primary fuel pump relay. Fuel is transfered from the secondary pump into the front tank to balance the fuel levels in both tanks depending on fuel level differences. The secondary fuel pump relay supply voltage is received from the primary fuel pump relay when the primary fuel pump is energized. This DTC is set when the secondary fuel pump is commanded on by the PCM and the PCM does not see a predetermined change in both the front and rear fuel level sensors.

Conditions for Running the DTC
    • The engine is running
    • The vehicle speed is 0 mph
    • No active fuel level sensor DTC's
    • The above conditions are met for 20 seconds before the secondary pump is commanded on
    • The secondary fuel pump is commanded on for 120 seconds

Conditions for Setting the DTC

The PCM does not detect a change of 4 Liters(1.06 gallons) in both the primary and secondary fuel level sensors with the secondary pump commanded on for 120 seconds.

Action Taken When the DTC Sets
    • The PCM stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.

Conditions for Clearing the DTC
    • A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
    • A history DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
    • Use a scan tool in order to clear the DTC.

Test Description

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

  1. It is necessary to command the primary fuel pump ON to supply voltage at the secondary fuel pump supply voltage cicuit.

Step

Action

Yes

No

1

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

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Observe the Freeze Frame and/or Failure records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame and/or Failure records data that you observed.

Does the DTC fail this ignition?

Go to Step 3

Go to Symptoms

3
  1. Turn OFF the ignition.
  2. Remove the Secondary Fuel Pump Relay.
  3. Turn ON the ignition leaving the engine OFF.
  4. Using a test lamp connected to ground, probe the secondary fuel pump relay supply voltage circuit at the secondary fuel pump relay connector.
  5. Using the Scan Tool, command the primary fuel pump ON.

Does the test lamp illuminate?

Go to Step 4

Go to Step 11

4

Using a test lamp connected to ground, probe the ignition 1 voltage circuit at the secondary fuel pump relay.

Does the test lamp illuminate?

Go to Step 5

Go to Step 14

5
  1. Turn OFF the ignition.
  2. Disconnect the PCM C2 harness connector. Refer to Powertrain Control Module Replacement
  3. Using a J 39200 DMM, test the continuity of the secondary fuel pump control circuit.

Does the DMM display continuity?

Go to Step 6

Go to Step 17

6

Test the secondary fuel pump control circuit for a short to voltage.

Did you find a problem?

Go to Step 18

Go to Step 7

7
  1. Using a fused jumper wire, jumper the ignition 1 voltage circuit and the secondary fuel pump supply voltage circuit. Refer to Using Fused Jumper Wires in Wiring Systems.
  2. Listen at rear of vehicle for secondary fuel pump running.

Does the secondary fuel pump run?

Go to Step 8

Go to Step 9

8
  1. Turn OFF the ignition.
  2. Swap the primary fuel pump relay and the secondary fuel pump relay.
  3. Attemp to start the engine.

Does the vehicle start and continue to run?

Go to Step 23

Go to Step 21

9
  1. Turn OFF the ignition.
  2. Disconnect the secondary fuel pump harness connector.
  3. Using a J 39200 DMM, test the secondary fuel pump supply circuit between the secondary fuel pump relay and the secondary fuel pump harness connector for continuity.

Does the DMM display continuity?

Go to Step 10

Go to Step 19

10

Using a test lamp connected to ground, probe the secondary fuel pump ground circuit at the secondary fuel pump harness connector.

Does the test lamp illuminate?

Go to Step 22

Go to Step 20

11

Using a test lamp connected to B+, probe the secondary fuel pump relay supply voltage at the relay connector.

Does the test lamp illuminate?

Go to Step 13

Go to Step 12

12

Repair the open in the secondary fuel pump relay supply voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 25

--

13

Repair the grounded secondary fuel pump relay supply voltage circuit between the primary fuel pump relay and the secondary fuel pump relay. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 25

--

14

Inspect the ignition 1 voltage fuse for an open.

Is the fuse open?

Go to Step 15

Go to Step 16

15

Repair the short to ground in the ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 25

--

16

Repair the open in the ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 25

--

17

Repair the open in the secondary fuel pump control circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 25

--

18

Repair the short to voltage in the secondary fuel pump control circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 25

--

19

Repair the open in the secondary fuel pump supply voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 25

--

20

Repair the open in the secondary fuel pump supply ground circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 25

--

21

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

Is the action complete?

Go to Step 25

--

22

Replace the secondary fuel level sensor assembly. Refer to Fuel Sender Assembly Replacement

Is the action complete?

Go to Step 25

--

23
  1. Inspect for poor connections at the PCM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. Repair the poor connections as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 25

Go to Step 24

24

Important: The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement

Is the action complete?

Go to Step 25

--

25
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 26

Go to Step 2

26

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to applicable DTC table

System OK