P064C - Glow Plug Control Module (GPCM) 1
System
Powertrain (Engine & Gearbox)
Technical Description
The control module has detected a fault in the Glow Plug Control Module (GPCM) 1 (P064C).
Multimeter Test Points & Nominal Values
| Test Point / Component | Measurement | Nominal Target Range | Test Condition |
|---|---|---|---|
| Glow Plug Control Module (GPCM) 1 – Permanent B+ Supply | Voltage (V) | 12.4 - 12.7 V (ignition OFF) / 13.5 - 14.7 V (engine running) | At module supply pins |
| Glow Plug Control Module (GPCM) 1 – Ignition-Switched Supply | Voltage (V) | 11.8 - 14.4 V | Ignition ON |
| Glow Plug Control Module (GPCM) 1 – Ground Connections Voltage Drop | Voltage (V) | < 0.1 V per ground point | Under load to battery negative |
| Glow Plug Control Module (GPCM) 1 – 5 V Reference Outputs | Voltage (V) | 4.95 - 5.05 V per circuit | Ignition ON, sensors unplugged one at a time |
At module supply pins
Ignition ON
Under load to battery negative
Ignition ON, sensors unplugged one at a time
Oscilloscope Waveform Analysis
500 ms/div, 5 V/divPossible Causes
Chafed or pinched wiring harness along the signal path to Glow Plug Control Module (GPCM) 1
Poor ground connection or excessive voltage drop (> 0.1 V) at the ground point for Glow Plug Control Module (GPCM) 1
Defective internal output driver or reference circuit in the control module for Glow Plug Control Module (GPCM) 1
Symptoms
Recommended Solution
Review freeze-frame environmental data and perform fundamental voltage-drop and resistance checks on the circuit.
Verify loaded supply voltage and harness terminal pins at Glow Plug Control Module (GPCM) 1.
Check circuit continuity and ground-side voltage drop (< 0.05 V) for Glow Plug Control Module (GPCM) 1.
Inspect module enclosure and connector headers for water ingress, fretting corrosion, or PCB thermal damage.
Mechanic's Tip
When facing a 5V reference supply DTC, never replace the module first. A shorted external sensor (such as A/C pressure or EGR position) drags down the shared 5V internal rail. Unplug sensors one by one until 5V recovers.