Powertrain Controls - ECM/PCM

Analog/Digital Internal PCM Control:

CIRCUIT DESCRIPTION
The Analog / Digital (A/D) multiplexer chip is an internal part of the Powertrain Control Module (PCM). The above exploded view of the "SFI-U" PCM shows sensor inputs to the A/D multiplexer that can affect driveability and diagnostics.

DIAGNOSTIC TROUBLE CODE (DTC) 86 WILL SET WHEN
Any of the above circuits is shorted to system voltage for 15 seconds.

ACTION TAKEN (PCM) WILL DEFAULT TO
The Malfunction Indicator Lamp (MIL) will become illuminated.

DTC 86 WILL CLEAR WHEN
A current DTC 86 will clear when 12 volts is no longer sensed on the above circuits. A History DTC 86 will clear after 50 consecutive ignition key cycles without a current DTC 86 being stored.

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 PCM connectors and terminals for proper location. DTC 86 will only set when the circuits leading to the A/D multiplexer, internal to the PCM gets shorted to 12 volts. If DTC 86 is intermitent, refer to "Diagnostic Aids" below.

DIAGNOSTIC AIDS
If DTC 86 is not present, all circuits leading to the PCM that are connected to the A/D multiplexer should be checked for an intermittent short to 12 volts. 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 12 volts will show erratic changes in data on the Tech 1 (or equivalent scan tool).