Loss of communication with TECU
Step 1:
Turn off the key.
Disconnect the negative battery cable.
Disconnect the TECU connector.
Unplug the engine ECM connector containing J1939 Data-Link.
Measure ohms between:
TECU Pin 2 and engine ECM pin for J1939 (-)
TECU Pin 2 and ground.
If Pin 2 to engine ECM has 0 to 0.3 ohms and Pin 2 to ground is OL, proceed to Step 2.
If ohms are outside range, fix J1939 Data-Link Harness between engine ECM and TECU. Clear codes and cycle key.
Step 2:
Turn off the key.
Measure ohms between:
TECU Pin 3 and engine ECM pin for J1939 (+)
TECU Pin 3 and ground.
If Pin 3 to engine ECM has 0 to 0.3 ohms and Pin 3 to ground is OL:
If J1939 Lite is present, go to Step 4.
If no J1939 Lite, go to Step 3.
If ohms are outside range, fix J1939 Data Link Harness between engine ECM and TECU. Clear codes and cycle key.
Step 3:
Turn off the key.
Measure ohms between TECU connector Pin 1 and engine ECM pin for J1939 shield.
If Pin 1 to engine ECM has 0 to 0.3 ohms, proceed to Step 4.
If ohms are outside range, repair J1939 Data-Link Harness between engine ECM and TECU. Clear codes and cycle key.
Step 4:
Turn off the key.
Measure ohms between TECU connector Pin 2 and Pin 3.
If ohms between Pin 2 and Pin 3 are 50 to 70 ohms, clear codes and cycle key.
If ohms are over 70 ohms, repair missing/out-of-range terminating resistors on OEM J1939 Data Link Harness. Clear codes and cycle key.
If ohms are under 50 ohms, repair J1939 Data Link between engine ECM and TECU. Clear codes and cycle key.
TROUBLESHOOTING SHACK 