- Powertrain/On-Board Diagnostic System Check

Diagnostic Chart:

PCM Circuit:

CIRCUIT DESCRIPTION
The On-Board Diagnostic System Check is an organized approach to identifying a problem created by an electronic engine control system malfunction. It must be the starting point for any driveability complaint diagnosis, because it directs the service technician to the next logical step in diagnosing the complaint. Understanding the chart and using it correctly will reduce diagnostic time and prevent the unnecessary replacement of good parts.

PRELIMINARY DIAGNOSTIC STEPS
1. Obtain an accurate description of the complaint and verify. Include filling out the Driveability Worksheet and Vehicle Repair History forms. Refer to Info Type/Technical Management Support/Vehicle Inspection Forms and Symptom Check List for these forms.

Perform Underhood Inspection:

a. Check vacuum hoses for splits, kinks, and proper routing.
b. Check ignition wires for cracking, hardness, and proper connections at both the distributor and spark plugs.
c. Check all wiring for proper connections, pinches, and cuts.
d. Check wiring harness for proper routing.
e. Check for missing components.

2. Check for manual updates, testing procedures, warranty and recall information.

3. Refer to PROM - Programmable Read Only Memory. PROM - Programmable Read Only Memory

TEST DESCRIPTION
The numbers below refer to circled numbers on the diagnostic chart.

1. This step is to determine if the Tech 1 scanner can establish communication with the Powertrain Control Module (PCM). If there is no communication between the PCM and the Tech 1, no data will be displayed. Faulty connections or an open PCM ignition feed to PCM connector D3 can also cause this problem.
2. Comparison of actual control system data with the typical values is a quick check to determine if any parameter is not within limits. Keep in mind that a base engine problem may substantially alter sensor values.
3. Installation of a scan tool will provide a ground path for the PCM and may hide a driveability complaint due to poor PCM grounds.
4. If multiple Diagnostic Trouble Codes (DTCs) are stored, start with the lowest numbered DTC first, unless the DTC chart indicates not to.
5. If the actual data is not within the typical values established, component Testing and Inspection procedures located under Powertrain Management will provide a functional check of the suspect component or system.

NOTE: This vehicle is equipped with a Powertrain Control Module utilizing an Electrically Erasable Programmable Read Only Memory (EEPROM). When diagnostics call for replacement of the PCM, the new PCM must be programmed. Refer to Powertrain Control Module/Service and Repair/EEPROM Programming. EEPROM Programming

DIAGNOSTIC AIDS
Inspect all related wiring and connections including the connections at the PCM, these may cause an intermittent malfunction. Check for damaged, corroded or pushed out terminals.