P067B - Cylinder 4 Glow Plug Control Circuit High
System
Powertrain (Engine & Gearbox)
Technical Description
The control module has detected a fault in the Cylinder 4 Glow Plug Control Circuit High (P067B). The signal is above the upper threshold, typically from an open circuit, poor connection, or a short to battery voltage. The fault is isolated to cylinder 4, positioned at the flywheel end (exposed to torsional vibration harmonics). This directly impacts individual cylinder volumetric efficiency, firing synchronization, and dedicated harness branch loading.
Multimeter Test Points & Nominal Values
| Test Point / Component | Measurement | Nominal Target Range | Test Condition |
|---|---|---|---|
| Cylinder 4 Glow Plug Control Circuit High – Permanent B+ Supply | Voltage (V) | 12.4 - 12.7 V (ignition OFF) / 13.5 - 14.7 V (engine running) | At module supply pins |
| Cylinder 4 Glow Plug Control Circuit High – Ignition-Switched Supply | Voltage (V) | 11.8 - 14.4 V | Ignition ON |
| Cylinder 4 Glow Plug Control Circuit High – Ground Connections Voltage Drop | Voltage (V) | < 0.1 V per ground point | Under load to battery negative |
| Cylinder 4 Glow Plug Control Circuit High – 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
Open circuit on signal wire, spread terminal pin, or short to power feed at Cylinder 4 Glow Plug Control Circuit High
Flywheel end torsional vibration (cylinder 4): High cyclic vibration harmonics from dual-mass flywheel and transmission input shaft transferred to terminal pins.
Rear cylinder coolant stagnation:Thermal stratification at cylinder head rear bulkhead and harness chaffing against bellhousing casting.
Chafed or pinched wiring harness along the signal path to Cylinder 4 Glow Plug Control Circuit High
Poor ground connection or excessive voltage drop (> 0.1 V) at the ground point for Cylinder 4 Glow Plug Control Circuit High
Defective internal output driver or reference circuit in the control module for Cylinder 4 Glow Plug Control Circuit High
Symptoms
Recommended Solution
Swap component on cylinder 4 over to cylinder 1 and clear DTCs to confirm if fault follows.
Inspect wiring harness brackets against transmission bellhousing casting and rear engine mount for vibration chafing.
Measure signal terminal voltage with ignition ON and sensor unplugged to determine if ECM pull-up is active or harness is shorted to 12V.
Verify loaded supply voltage and harness terminal pins at Cylinder 4 Glow Plug Control Circuit High.
Check circuit continuity and ground-side voltage drop (< 0.05 V) for Cylinder 4 Glow Plug Control Circuit High.
Inspect module enclosure and connector headers for water ingress, fretting corrosion, or PCB thermal damage.
Mechanic's Tip
Pro-tip for cylinder 4: Cylinder 4 sits closest to the flywheel and absorbs powertrain torsional harmonics. Inspect wiring closely for chafing against bellhousing brackets.