P06FD means signals or messages from glow plug control module 2 arrive at the engine module but are implausible – wrong duty cycle or pattern, feedback not matching the command, or single messages timing out. It is the counterpart of P0684 for module 1; Saab's Bosch-based diesels, for example, expect the feedback signal to be inverse to the command line. No manufacturer document available to us uses a second glow module – Ford's and GM's V8 diesels drive all eight plugs from one; the code suits systems with one module per cylinder bank. The description follows module 1 (P0684). A missing signal or open line is P06FC, a lost bus link usually U0106. The plugs of module 2 then heat poorly or not at all, typically on one bank.
Low severity. Can I keep driving?You can keep driving, although cold starts will be harder. Avoid cranking the starter repeatedly on cold days.
Symptoms
- Check engine light, possibly glow plug/wait-to-start lamp
- Hard cold start, long cranking in frost
- Rough cold idle and white smoke, often one cylinder bank only
- Usually no symptoms when warm
Most likely causes
- Loose contact or contact resistance in the feedback or bus line
- Ground offset between module and engine module from glow currents
- Software mismatch between modules or module faulty
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P06FD means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 6: Control modules and outputs
- FD: Specific fault in that system
Frequently asked questions
Can I keep driving with code P06FD?
You can keep driving, although cold starts will be harder. Avoid cranking the starter repeatedly on cold days.
What causes code P06FD?
The most common causes are: loose contact or contact resistance in the feedback or bus line; ground offset between module and engine module from glow currents; software mismatch between modules or module faulty.
Related codes
- P0684Glow Plug Control Module 1 to PCM Communication Circuit Range/Performance
- P06FCGlow Plug Control Module 2 to PCM Communication Circuit
- P06F5Glow Plug Control Module 2
- U0106Lost Communication with Glow Plug Control Module
Sources
- law.cornell.edu: 13 CCR 1968.2
- fordservicecontent.com: obd summary diesel 2023
- gsi.ext.gm.com: 18OBDG04 Engine Diagnostics
- patents.google.com: US9612166
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.