U0106

Code

Generic U — Network/User

Lost Communication With Glow Plug Control Module 1

Brand: Generic

Type: U — Network/User

Views: UK: 34 EN: 103 RU: 49

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open or short in CAN bus wiring (CAN High / CAN Low)
Glow plug control module power supply fuse or relay blown
Poor or corroded connector or pin at the module
Faulty ground connection at the module
Failed glow plug control module
Network termination resistor missing or damaged

Symptoms

Glow plug system warning light or diesel preheat warning
Difficult cold starts or extended crank time
Other modules reporting related U-codes (multiple lost-communication codes)
No communication with glow plug control module when scanning
Possible reduced engine performance or limp-home behavior if ECU limits functions

What to check

Attempt communication with glow plug control module using a scan tool; note presence/absence and any other network codes
Check battery voltage (should be ~12.6 V at rest, >12 V with key on) and health
Inspect fuses and relays supplying the glow plug control module
Visually inspect wiring harness and connectors at the module for corrosion, damage, or pushed-out pins
Check module supply and ground continuity (power with key on and good ground)
Measure CAN bus voltages at the module connector (CAN H and CAN L) with key on

Signal parameters

Battery/ignition supply to module: ~12 V (key on/run)
Ground continuity: near 0 ohms to chassis ground
CAN High (key on, idle): ~2.5 V (nominal), dominant ~3.5 V
CAN Low (key on, idle): ~2.5 V (nominal), dominant ~1.5 V
Differential CAN: ~0 V idle, differential pulses during communication; expected regular frames when module healthy
Termination resistance: ~60 ohms across CAN H and CAN L (with power off)

Diagnostic algorithm

Retrieve freeze frame data and all stored U-codes. Note conditions when code set.
Confirm battery voltage and charge if low. Clear DTCs and attempt to reproduce. Low voltage can cause network dropouts.
Use a scan tool to list modules on the CAN network. Verify whether Glow Plug Control Module 1 appears.
Visually inspect the glow plug control module connector and harness for damage, corrosion, pushed-out or bent pins.
With ignition ON (engine off), verify module power pin is ~12 V and ground pin has good continuity to chassis ground.
Measure CAN H and CAN L at the module connector with key on. Confirm idle voltages (~2.5 V each) and check for communication signals with a scope or CAN bus analyzer.
Check termination resistance across CAN H and CAN L with power off (approx. 60 ohms). Replace termination resistors or repair wiring if out of spec.
Inspect and test related fuses and relays. Replace any blown components and retest communication.
If wiring, power and termination are good but no communication, attempt to communicate using a different good module location or harness pin to rule out instrument cluster/scan tool issues.
If wiring and network appear healthy, consider replacing or reflashing the Glow Plug Control Module. Reprogram or adapt the replacement per manufacturer procedures.
After repair, clear codes and perform functional test (cold start cycles) and a road test to ensure code does not return.

Likely causes

Damaged CAN wiring between PCM and glow plug control module (chafed, pinched, rodent damage)
Module supply fuse removed/blown or relay contact failure
Corroded or loose module connector pins preventing CAN or power/ground
Bad ground strap at engine or module mounting point
Module internal failure (electronics) preventing CAN transmit/receive
Missing or open 60 ohm CAN termination across CAN H and CAN L

Fault status

⚠️ Status

Lost Communication With Glow Plug Control Module 1 — no CAN messages received from Glow Plug Control Module 1 or module not responding to diagnostic requests.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-3 hours