DTC 0421. GMC Truck GMC T-Series Medium Duty Truck F6/F7/F8 2001

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC T-Series Medium Duty Truck F6/F7/F8 🢒 DTC 🢒 DTC 0421

Circuit Description

The pressure control valve (PCV) is used to adjust the supply pump discharge amount to adjust common rail pressure. The discharge amount from the supply pump to the common rail is determined by continuity timing to the PCV. The PCV relay is used to supply an electric current to the PCV.

Conditions for Setting the DTC

The PCV driving voltage is abnormal when the ignition is OFF causing the PCV circuit to turn OFF.

Action Taken When the DTC Sets

The engine control module (ECM) sets DTC 0421 memory.

Conditions for Clearing the MIL/DTC

•	The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

•	A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

•	A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

•	Clear the MIL and the DTC with a scan tool.

DTC 0421 can be cleared by using the Clear Info option on the Tech 2 or by using the Diag Clear Switch.

Diagnostic Aids

Inspect for poor connections at the PCV relay. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal-to-wire connections.

DTC 0421 PCV Relay (R/L) System Error

Step

Action

Values

Yes

Schematic Reference: Engine Controls Schematics

Does DTC 0421 set with the ignition ON or with the engine operating?

Go to Step 2

Go to Diagnostic Aids

Turn the ignition OFF.
Disconnect the PCV harness.
Measure the voltage at the ECM connector C2 between the following points:

•	Between pin number 21, 22 of PCV 1 and pin number 82 of the ECM.

•	Between pin number 31, 32 of PCV 2 and pin number 82 of the ECM.

Does the voltage measure near the specified value?

12 V

Go to Step 5

Go to Step 3

Temporarily jumper the signal and ground pin together at the PCV.

Is DTC 0421 set?

Go to Step 4

Go to Step 7

Is DTC 0421 set?

Go to Step 8

System OK

Remove the PCV relay.
Measure the resistance between contact point 5 and 1.

Does the resistance measure more than the specified value?

100M ohms

Go to Step 6

Go to Step 7

Turn the ignition OFF.
Disconnect the PCV harness from the PCV, PCV relay, and the ECM connector C2.
Measure the voltage between pin number 1 at the PCV relay and pin number 82 at the ECM .

Does the voltage measure less than the specified value?

1 V

Go to Step 7

Replace the PCV harness or relay.

Did you complete the replacement?

Go to Step 9

Replace the ECM.

Did you complete the replacement?

Go to Step 9

Clear the memory.

Does DTC 0421 set?

Go to Step 2

System OK