DTC P066A-P066F, P0671-P0676, or P067A-P067F

Engine Controls and Fuel - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 5500364 Diagnostic Instructions Perform the Diagnostic System Check prior to using this diagnostic procedure: Diagnostic System Check - Vehicle Review the description of Strategy Based Diagnosis: Strategy Based Diagnosis An overview of each diagnostic category can be found here: Diagnostic Procedure Instructions DTC Descriptor DTC P066A Cylinder 1 Glow Plug Control Circuit Low DTC P066B Cylinder 1 Glow Plug Control Circuit High DTC P066C Cylinder 2 Glow Plug Control Circuit Low DTC P066D Cylinder 2 Glow Plug Control Circuit High DTC P066E Cylinder 3 Glow Plug Control Circuit Low DTC P066F Cylinder 3 Glow Plug Control Circuit High DTC P0671 Cylinder 1 Glow Plug Control Circuit DTC P0672 Cylinder 2 Glow Plug Control Circuit DTC P0673 Cylinder 3 Glow Plug Control Circuit DTC P0674 Cylinder 4 Glow Plug Control Circuit DTC P0675 Cylinder 5 Glow Plug Control Circuit DTC P0676 Cylinder 6 Glow Plug Control Circuit DTC P067A Cylinder 4 Glow Plug Control Circuit Low DTC P067B Cylinder 4 Glow Plug Control Circuit High DTC P067C Cylinder 5 Glow Plug Control Circuit Low DTC P067D Cylinder 5 Glow Plug Control Circuit High DTC P067E Cylinder 6 Glow Plug Control Circuit Low DTC P067F Cylinder 6 Glow Plug Control Circuit High Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performanc
Control — Terminal 1/A @ E12A Glow Plug 1	P066A	P0671	P066B	—

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performanc
Control — Terminal 1/A @ E12B Glow Plug 2	P066C	P0672	P066D	—
Control — Terminal 1/A @ E12C Glow Plug 3	P066E	P0673	P066F	—
Control — Terminal 1/A @ E12D Glow Plug 4	P067A	P0674	P067B	—
Control — Terminal 1/A @ E12E Glow Plug 5	P067C	P0675	P067D	—
Control — Terminal 1/A @ E12F Glow Plug 6	P067E	P0676	P067F	—

Typical Scan Tool Data Cylinder 1-6 Glow Plug Control Circuit High Test Status

Circuit	Short to Ground	Open	Short to Voltage
Operating Conditions: Ignition On Parameter Normal Range: Not Run or Okay
Control — Terminal 1/A	—	—	Malfunction

Cylinder 1-6 Glow Plug Control Circuit Low Test Status

Circuit	Short to Ground	Open	Short to Voltage
Operating Conditions: Ignition On Parameter Normal Range: Not Run or Okay
Control — Terminal 1/A	Malfunction	—	—

Cylinder 1–6 Glow Plug Control Circuit Open Test Status

Circuit	Short to Ground	Open	Short to Voltage
Operating Conditions: Ignition On Parameter Normal Range: Not Run or Okay
Control — Terminal 1/A	—	Malfunction	—

For an overview of the component/system, refer to: Glow Plug System Description

Circuit	Description
Control	The output circuit is switched to 10 V to activate the component. When the output is commanded On, the voltage can range between 4.7 and 10 V. The output is PWM controlled.

Component	Description
E12 Glow Plug	Glow plugs are electric heating devices in the combustion chambers of diesel engines. Depending on ambient and coolant temperature the glow plugs are activated for different times: Before and after the engine was started Before the engine has started Not at all The glow time indicator needs to go off after the engine has started to indicate that the system is working properly, even when the glow plugs are still active. To activate the glow plugs, the engine control module itself supplies the glow plugs with voltage. This voltage is regulated so that the glow plugs don’t overheat.
K20 Engine Control Module	The control module contains a microprocessor used to process input data to control outputs. The control module controls a series of actuators to ensure optimal engine performance. The control module does this by reading values from a variety of sensors, interprets the data and adjusts the engine actuators accordingly.

Conditions for Running the DTC Ignition and Start Switch Signal = On Engine Cranking = No E12 Glow Plug = On Battery Voltage = Greater than 7 V @ K20 Engine Control Module Battery Voltage = Ignition and Start Signal @ K20 Engine Control Module Frequency the DTC runs = Continuously — After the running conditions are met Conditions for Setting the DTC Control Circuit = Commanded state does not match the actual state — For greater than 1 s Actions Taken When the DTC Sets DTCs listed in the DTC Descriptor category = Type B DTC Conditions for Clearing the DTC DTCs listed in the DTC Descriptor category = Type B DTC Diagnostic Aids { Cadillac } If F5UD Fuse is open, DTC P066A, P066C, P066E, P067A, P067C, P067E will set. { Chevrolet / GMC } If F5BA Fuse is open, DTC P066A, P066C, P066E, P067A, P067C, P067E  will set. Reference Information Schematic Reference Engine Controls Schematics Connector End View Reference Master Electrical Component List Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs DTC Type Reference Powertrain Diagnostic Trouble Code (DTC) Type Definitions Scan Tool Reference Control Module References Circuit/System Verification

1. Ignition » On / Vehicle » In Service Mode
2. Verify DTC P066A, P066C, P066E, P067A, P067C, P067E is not set. — All ⇒ If all of the DTCs are set Refer to: Circuit/System Testing — Test 1 ⇓ If all of the DTCs are not set
3. Verify DTC P066A-P066F, P0671-P0676, or P067A-P067F is not set. ⇒ If any of the DTCs are set Refer to: Circuit/System Testing — Test 2 ⇓ If none of the DTCs are set
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 data. Verify the DTC does not set. ⇒ If the DTC sets Refer to: Circuit/System Testing ⇓ If the DTC is not set
5. All OK. Circuit/System Testing Test 1
6. Ignition/Vehicle & All vehicle systems » Off
7. Disconnect the electrical connector: X1 @ K20 Engine Control Module
8. Test for battery voltage between the test points: B+ circuit terminal 1 & Ground ⇒ If less than battery voltage 3.1. Test for less than 2 Ω between the test points: { Cadillac } B+ circuit terminal 1 & Output terminal @ F5UD Fuse { Chevrolet / GMC } B+ circuit terminal 1 & Output terminal @ F5BA Fuse ⇒ If 2 Ω or greater » Repair the open/high resistance in the circuit. ⇓ If less than 2 Ω 3.2. Test for infinite resistance between the test points: B+ circuit terminal 1 & Ground ⇒ If less than infinite resistance » Repair the short to ground on the circuit. ⇓ If infinite resistance 3.3. Verify the fuse is OK and there is voltage at the fuse. ⇒ If a condition exists » Repair or replace as necessary ⇒ If no condition exists » Replace the component: K20 Engine Control Module ⇓ If battery voltage
9. Connect a DMM between the test points: B+ circuit terminal 1 & Ground
10. Verify the DMM displays the following: Battery Voltage = The value should not spike or drop out. Perform the action while monitoring the DMM: Wiggle the harness and connector: X5–A @ X50B Battery Distribution Engine Compartment Fuse Block ⇒ If the value spikes or drops out Repair as necessary » Wiring / Terminal(s) / Electrical Connector(s) / Fuse ⇓ If the value does not spike or drop out
11. Replace the component: K20 Engine Control Module Test 2
12. Ignition/Vehicle » Off
13. Disconnect the appropriate electrical connector: E12 Glow Plug
14. Ignition » On / Vehicle » In Service Mode
15. Connect a test lamp between the test points: Control circuit terminal 1/A & Ground
16. Perform the scan tool control function: Glow Plugs » On and Off Verify the test lamp turns On and Off. ⇒ If the test lamp is always Off 5.1. Ignition/Vehicle » Off & Remove » Test lamp 5.2. Disconnect the electrical connector: X1 @ K20 Engine Control Module 5.3. Test for infinite resistance between the test points: Control circuit terminal 1/A @ Component harness & Ground ⇒ If less than infinite resistance » Repair the short to ground on the circuit. ⇓ If infinite resistance 5.4. Test for less than 2 Ω between the test points: Control circuit terminal 1/A @ Component harness & The other end of the circuit @ Control module harness ⇒ If 2 Ω or greater » Repair the open/high resistance in the circuit. ⇒ If less than 2 Ω » Replace the component: K20 Engine Control Module ⇒ If the test lamp is always On 5.1. Ignition/Vehicle » Off & Remove » Test lamp 5.2. Disconnect the electrical connector: X1 @ K20 Engine Control Module 5.3. Ignition » On / Vehicle » In Service Mode 5.4. Test for less than 1 V between the test points: Control circuit terminal 1/A @ Component harness & Ground ⇒ If 1 V or greater » Repair the short to voltage on the circuit. ⇒ If less than 1 V » Replace the component: K20 Engine Control Module ⇓ If the test lamp turns On and Off
17. Test or replace the component: E12 Glow Plug Component Testing
18. Ignition/Vehicle » Off
19. Disconnect the appropriate electrical connector: E12 Glow Plug
20. Test for less than 1.8 Ω between the test points: Control terminal 1/A & The component’s housing ⇒ If 1.8 Ω or greater Replace the component: E12 Glow Plug ⇓ If less than 1.8 Ω
21. All OK. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification Battery Distribution Engine Compartment Fuse Block Replacement — F5BA Fuse Glow Plug Replacement - Cylinder 1 Glow Plug Replacement - Cylinder 2 Glow Plug Replacement - Cylinder 3 Glow Plug Replacement - Cylinder 4 Glow Plug Replacement - Cylinder 5 Glow Plug Replacement - Cylinder 6 For control module replacement, programming, and setup refer to: Control Module References