DTC 86

Internal ECM A/D Control:

CIRCUIT DESCRIPTION
The A/D multiplexer chip is an internal part of the ECM. Some ECM sensor inputs lead to the A/D multiplexer. If any one of those circuits should short to B+ for a time of greater than or equal to 15 seconds, the A/D error diagnostic will set.


TEST DESCRIPTION
For DTC 86, check for any DTCs that are stored and refer to those charts. If no other DTCs are stored, check all ECM connectors and terminals for proper location. DTC 86 will set only when the circuits leading to the A/D multiplexer, internal to the ECM gets shorted to B+. If DTC 86 is intermittent, refer to "Diagnostic Aids".

DIAGNOSTIC AIDS:
If DTC 86 is not present, all circuits leading to the ECM that are connected to the A/D multiplexer should be checked for an intermittent short to B+. Move the harnesses of each component and watch the scan data on the Tech 1 (or equivalent) scan tool. The circuit that is shorted to B+ will show erratic changes in data on the Tech 1 (or equivalent) scan tool.