What it means
The drive line from the PCM to glow plug control module 1 is stuck low — short to ground. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The PCM sends a control signal to glow plug control module 1 to request glow plug operation. P0383 sets when the PCM detects that this control line is held below its expected level, commonly because it is shorted to ground.
Common causes
Most likely first.
- Short to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Glow plug warning light on (often orange coil symbol)
- Hard cold start or no start in cold weather
- White smoke from exhaust during warm-up
How to diagnose it
- Record freeze-frame data and check whether the PCM commanded glow plug module 1 when the low control condition was detected.
- Inspect the control wire between the PCM and glow plug control module 1 for chafing, damaged insulation, corrosion, or loose terminals.
- Check the module 1 connector and its power and ground connections for corrosion or poor contact.
- With the circuit isolated as specified by the manufacturer, test the PCM-to-module control line for a short to ground and continuity.
- If the circuit and module connections pass, test glow plug control module 1 and the PCM control output against the manufacturer's specification.
Common fixes
- Repair chafed control wiring that is shorting to ground.
- Clean and secure corroded or loose terminals at glow plug control module 1.
- Repair a damaged section of the PCM-to-module harness.
- Replace glow plug control module 1 or repair the PCM control output only if testing confirms the fault.
Can I keep driving?
Glow plug module 1 may not receive a reliable command, which can cause difficult cold starts and white smoke during warm-up. Avoid repeated extended cranking in cold weather.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.