Code
P1642
DAEWOO
P — Powertrain
Serial comm. error - nonimmob
AI status
Completed
Completed
100%
Causes
- Open, short, or high resistance in CAN/LIN wiring or connectors
- Failed or intermittent control module (non‑immobilizer module such as BCM, instrument cluster, etc.)
- Low or unstable battery voltage or poor ground
- Missing or damaged termination resistor on CAN bus
- Blown fuse or loss of power supply to one of the networked modules
- Aftermarket electronics interfering with the serial bus
Symptoms
- MIL (Check Engine) lamp illuminated
- Intermittent or permanent loss of functions controlled by the affected module (e.g., instrument cluster, doors, lights)
- No communication with one or more modules in the scan tool
- Crank/no‑start or starting problems if critical module is not communicating
- Erratic or intermittent electrical behavior
What to check
- Read all stored codes and module status with a capable scan tool; note which modules show 'no communication'
- Check and record battery voltage (key on and cranking); confirm >12.4 V at rest and >10 V during cranking
- Visually inspect harnesses, connectors, and grounds for corrosion, looseness, or damage
- Verify fuses and power feeds to the affected modules
- Check CAN/LIN bus for proper termination (approx. 60 ohm across CAN_H and CAN_L) and for short to ground or battery
- Use scan tool to monitor live data and communication lines to confirm intermittent or permanent loss
Signal parameters
- CAN bus recessive idle ≈ 2.5 V on each CAN line (typical); differential ≈ 0 V (recessive)
- CAN typical data rates: 250 kb/s or 500 kb/s depending on vehicle
- LIN typical baud rate ≈ 19.2 kb/s (if vehicle uses LIN)
- Termination resistance across CAN_H and CAN_L ≈ 60 ohms (two 120 ohm resistors in parallel)
- Look for error frames, timeouts or missing message IDs when monitoring bus with scan tool or scope
Diagnostic algorithm
- Retrieve freeze frame and all codes; note which modules report communication loss.
- Confirm battery health and secure/clean battery positive, negative and main chassis ground connections.
- Visually inspect connectors and wiring for damage, corrosion or loose pins at ECM, BCM, instrument cluster and any gateway module.
- Verify power and ground at the suspected non‑communicating module(s); check associated fuses and relays.
- Using a scan tool, list available modules and attempt communication; identify which module(s) are not responding.
- Measure termination resistance across CAN_H and CAN_L with power off; expected ≈ 60 ohms. Check for shorts to Vb or ground on each bus wire.
- If intermittent, backprobe CAN/LIN lines with an oscilloscope and observe message traffic and error frames while operating affected functions.
- Isolate the fault by disconnecting suspected modules one at a time while monitoring bus to see if communication restores.
- Repair or replace damaged wiring, connectors or fuses. Replace failed module only after confirming wiring and power/ground are correct.
- After repair or module replacement, clear codes, perform any required reprogramming or module initialization, then verify normal communication and that the code does not return.
Likely causes
- Corroded connector or pin at ECM, BCM, or gateway module
- Damaged CAN/LIN wiring harness (pinched, chafed, or shorted)
- Failed body control module (BCM) or instrument cluster
- Weak battery or poor battery terminal/ground connection
- Open or shorted CAN termination resistor (~60 ohm total)
Fault status
Status
ECM detected a serial communication interruption with a non‑immobilizer module on the vehicle network and stored code P1642. The fault indicates messages expected by the ECM were not received or were corrupted; affected vehicle functions may be disabled or intermittent.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Repair manuals
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