Powertrain, generic · Computer and auxiliary outputs

P06FD Glow Plug Control Module 2 to PCM Communication Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

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

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

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–600
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

glow plug control module 2glow plug feedback lineengine control module

Related codes

P0684P06FCP06F5U0106

References: law.cornell.edu, fordservicecontent.com, gsi.ext.gm.com, patents.google.com.