Bus and Diagnostics Communication

P1921
No Bus data From TRIONIC.

Fault symptoms
No bus communication with Trionic

Condition
The following conditions are applicable:

TCM:
^ The automatic transmission input shaft speed exceeded 200 rpm once during the present driving cycle
^ No communication for 4 seconds.

Diagnostic help
Some of the following symptoms may be observed:
^ Diagnostic trouble codes P1623, P1622, P1901 or P1902 in Trionic (if Trionic can be contacted)
^ Additional diagnostic trouble code in the TCM (P1902).
^ Misfiring.
^ Engine fails to start.
^ Automatic transmission in Limp-Home mode (CHECK GEARBOX lamp ON).






Checking the wiring harness
Jiggle the wiring harness at several points and in different directions to detect intermittent breaks and short-circuits in the leads. Observe the multimeter, test lamp or diagnostic tool during the test.