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Home >> Pontiac >> 1995 >> Sunfire L4-138 2.3L DOHC VIN D MFI >> Repair and Diagnosis >> Transmission and Drivetrain >> Automatic Transmission/Transaxle >> Testing and Inspection >> Initial Inspection and Diagnostic Overview >> Diagnostic System Check

Diagnostic System Check

OBD Chart:




OBD Chart (Cont):




MIL And DTC Circuits:






CIRCUIT DESCRIPTION
The On-Board Diagnostic (OBD) 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 PCM driveability complaint. Understanding the chart and using it correctly will reduce diagnostic time and prevent the unnecessary replacement of good parts.

DIAGNOSTIC AIDS
The engine runs OK, check for the following:

- Faulty Instrument Panel Cluster (IPC).
- CKT 419 open.
- ERLS fuse blown.

Engine cranks but will not run, check for the following:

- Continuous battery - fuse open.
- PCM ignition feed fuse open.
- Battery CKT 480 to PCM open.
- Ignition CKT 639 or CKT 1020 to PCM open.
- Poor terminal connection to PCM.
- Poor PCM ground.

TEST DESCRIPTION
Number(s) below refer to the step number(s) on the Diagnostic Chart.

2. Most of the diagnostic procedures use a scan tool to aid diagnosis, therefore serial data must be available.
3. This step is a check for proper operation of the Malfunction Indicator Lamp (MIL). The MIL should momentarily flash "OFF" then stay "ON".
4. Although the PCM is powered up, an "Engine Cranks But Will Not Run" symptom could exist because of a PCM or a system problem.
5. Exercise the following sensors for proper operation:

- ECT sensor for initial coolant temperature reading close to ambient, then observe the raise in temperature to operating temperature while the engine is warming up.
- TP sensor for proper sweep from 0% to 100%.
- MAP sensor for quick changes during changes in various engine loads.
- The IAC valve for proper idle control and observe for proper transitions while operating high load components, such as A/C control, or Park to Drive transitions.
- The front O2S for proper r/l or l/r sweep operation.

Exercising the various sensors can be a crucial step in correctly diagnosing any driveability concern. Careful observation of these sensors during engine warm-up may reveal a slow responding sensor or a sensor that malfunctions only on a small part of its range. After the engine is up to normal operating temperature, 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 (i.e. advanced cam timing) may substantially alter sensor values.

6. This will isolate if the customer complaint is a MIL or a driveability problem with no MIL. An invalid DTC may be the result of a faulty scan tool.
7. Using a known good vehicle equipped with the same type of body style, powertrain, and PCM will determine if the scan tool or vehicle is faulty.
9. Instructions for reprogramming the PCM is located at Powertrain Control Module / Service and Repair.
10. If replacing the PCM there are a few procedures that need to be performed. These procedures are explained under PCM / Service and Repair.
13. When a DTC is cleared, a PCM is disconnected from a vehicle, a PCM is replaced, or if a battery is disconnected, the "System Status" data resets its test run data to "NO." Performing the OBD II Drive Cycle not only runs all of the diagnostics, it also sets the "System Status" data to "YES" after its corresponding test runs. The "System Status" data list is for the Inspection/Maintenance regulations.
15. If a repair involves clearing DTC(s) from the PCM, the repair needs to be verified by operating the vehicle in the parameters set in "Conditions for Setting the DTC" for the DTC to be verified. Operating the vehicle using the parameters set in the "Conditions for Setting the DTC should exercise the diagnostic to be verified and determine a pass or fail of the particular diagnostic being verified.

NOTE: If the DTC to be verified has System Status data, the System Status will change to Not Run for the respective diagnostic.

16. When DTCs are cleared, "Test Not Run SCC", which stands for test not run since code clear, fills up with a list of diagnostics that have not been run. While performing the OBD II drive cycle, the list of diagnostics should shrink until all the diagnostics have run and the PCM determined PASS or FAIL.

NOTE: The System Status data will change to "Not Run" for all system status data when one of the following is performed.

- PCM disconnect.
- PCM replacement.
- Battery disconnect.

If any of the above actions are performed, the OBD II drive cycle needs to be performed. System Status (I/M 240) explains the OBD II drive cycle. System Status (I/M 240)
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