DTC P0231 Fuel Pump Feedback Circuit Low Voltage. GMC Truck GMC K Pickup

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC K Pickup - 4WD 🢒 Engine 🢒 Engine Controls - 6.5L 🢒 DTC P0231 Fuel Pump Feedback Circuit Low Voltage

Refer to Engine Controls Schematics

Circuit Description

The status of the lift pump is monitored by the PCM. This signal is also used to store a DTC if the fuel pump relay is defective or fuel pump voltage is lost while the engine is running. There should be about 12 volts on circuit 120 during glow plug cycle.

Conditions for Running the DTC

•	The PCM performs this DTC diagnostic continuously.

•	The fuel lift pump is commanded ON.

Conditions for Setting the DTC

•	The difference between ignition voltage and fuel pump voltage is more than 4 volts.

•	All diagnostic conditions met for 2 seconds.

Action Taken When the DTC Sets

•	The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.

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The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records will store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.

Conditions for Clearing the MIL/DTC

•	The PCM will turn the MIL off after three consecutive trips without a fault condition.

•	A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures

•	The use of a scan tool.

Diagnostic Aids

This DTC will not check the fuel pump operation.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

This step checks the fuel lift pump circuit.

Step	Action	Value(s)	Yes	No
1	Important: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame and failure records for reference. The control module's data is deleted once the Clear Info function is used. 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	Connect a Scan tool. Turn the ignition ON. With the scan tool, command the fuel pump ON. Does the scan tool indicate the fuel pump is operating?	--	Go to Diagnostic Aids	Go to Step 3
3	Turn the ignition OFF. With a J 39200 connected to ground, backprobe the fuel lift pump signal circuit at the PCM. Probe the fuel pump test terminal with a fused jumper to B+. Is the voltage at the specified value?	B+	Go to Step 8	Go to Step 4
4	Remove the fuel pump relay. Verify the J 39200 is still connected. From underneath the U/H relay center, probe the A3 terminal with a fused jumper to B+. Is the voltage at the specified value?	B+	Go to Step 5	Go to Step 6
5	Check for a proper connection at the fuel pump relay center. If a problem is found, repair the problem as necessary. Was a problem found?	--	Go to Step 19	Go to Step 18
6	Check for an open or short to ground on the fuel pump signal circuit. If a problem is found, repair the problem as necessary. Was a problem found?	--	Go to Step 19	Go to Step 7
7	Check for proper connections at the PCM and at the relay center. If a problem is found, repair the problem as necessary. Was a problem found?	--	Go to Step 19	Go to Step 16
8	Remove the fuel pump relay. Turn the ignition ON. Connect a test light to ground. Probe the fuel pump relay harness connector terminal B1. Is the test light ON?	--	Go to Step 10	Go to Step 9
9	Repair the open in the battery feed circuit to the fuel pump relay. Is the action complete?	--	Go to Step 19	--
10	Connect a test light between terminal number B1 and terminal number A1 of the fuel pump relay harness connector. Is the test light ON?	--	Go to Step 12	Go to Step 11
11	Repair the open fuel pump relay ground circuit. Is the action complete?	--	Go to Step 19
12	Turn the ignition OFF. Connect a test light between terminal number B3 of the fuel pump relay harness connector and ground. Monitor the test light. Turn the ignition ON. Does the test light come ON during the glow plug cycle and then go OFF after the glow plug cycle is complete?	--	Go to Step 13	Go to Step 14
13	Turn the ignition OFF. Connect a test light to ground, backprobe the fuel lift pump signal circuit at the PCM. Monitor the test light. Turn the ignition ON. Does the test light come ON during the glow plug cycle and then go OFF after the glow plug cycle is complete?	--	Go to Step 16	Go to Step 17
14	Check for an open or short to ground in the circuit from the fuel pump relay harness connector terminal number B3 and PCM. Was a problem found?	--	Go to Step 15	Go to Step 16
15	Repair the open or short to ground in the fuel pump relay control circuit. Is the action complete?	--	Go to Step 19	--
16	Replace the PCM. Important: The new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is the action complete?	--	Go to Step 19	--
17	Check for proper connections at the fuel pump relay connector. Was a problem found?	--	Go to Step 19	Go to Step 18
18	Replace the fuel pump relay. Refer to Fuel Pump Relay Replacement . Is the action complete?	--	Go to Step 19	--
19	Using the scan tool, clear the DTCs. Start the engine. Allow the engine to idle at normal operating temperature. Select DTC and the Specific DTC function. Enter the DTC number which was set. Operate the vehicle, with the Condition for Setting this DTC, until the scan tool indicates the diagnostic Ran. Does the scan tool indicate the diagnostic Passed?	--	Go to Step 20	Go to Step 2
20	Does the scan tool display any additional undiagnosed DTCs?	--	Go to the Applicable DTC Table	System OK