Refer to
.
Circuit Description
The Powertrain On-Board Diagnostic System Check must be the starting
point for any driveability complaint diagnosis. Before using this procedure,
you should perform a careful visual/physical check of the PCM and engine grounds
for being clean and tight. The Powertrain On-Board Diagnostic System Check
is an organized approach to identifying a problem created by an electronic
engine control system malfunction.
MIL Operation
The Malfunction Indicator Lamp (MIL) is located on the instrument panel
(CHECK ENGINE) or (SERVICE ENGINE SOON). The MIL performs the following functions:
| • | It informs the driver that a problem has occurred and that the
vehicle should be taken for service as soon as possible. |
| • | As a bulb check and system check, the MIL will illuminate with
the ignition switch ON and the engine not running. when the engine is started,
the MIL will turn OFF. If the MIL remains ON, the self-diagnostic system has
detected a problem. If the problem goes away, the MIL will turn OFF in most
cases, but a diagnostic trouble code will remain stored. |
| • | If the MIL is illuminated, then the engine stalls, the MIL will
remain Illuminated so long as the ignition switch is ON. |
| • | Now, if the MIL is not
illuminated and
the engine stalls, the MIL will not illuminate until the ignition switch is
cycled OFF, then ON. |
Perform the Powertrain On-Board Diagnostic System Check first, when
the following conditions are present:
| • | When the MIL does not turn ON when the the ignition switch is
turned to the RUN position |
| • | When the MIL remains ON while the engine is running |
| • | When you suspect a driveability problem |
| • | When you suspect an emissions problem |
Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed through wire
insulation or a wire broken inside the insulation. Check for poor connections
or a damaged harness. Inspect the PCM harness and connectors for improper
mating, broken locks, improperly formed or damaged terminals, poor terminal
to wire connection, and damaged harness.
Test Description
Number(s) below refer to the Step number(s) on the Diagnostic Table:
-
The MIL should be ON steady with the key ON / engine OFF. If not, the
No Malfunction Indicator Lamp table should be used to isolate the malfunction.
-
This test ensures that the PCM is capable transmitting Class 2 serial
data to the DLC and that the Class 2 data circuit is not open or shorted.
If a problem is encountered and a malfunctioning scan tool is suspected, try
the scan tool on another vehicle to verify operation. If a DLC problem exists,
the DLC Diagnosis table should be used to diagnose the condition.
-
If the engine
will not start, the Engine Cranks But Will Not Run table should be used to
diagnose the condition.
-
The scan tool may display DTC(s) which are diagnosed
in 4T60-E / 4T65-E Automatic Transaxle Diagnosis
. Go to
Powertrain Control Module Diagnosis
for a complete list of DTC(s) supported by this vehicle
application. If multiple DTCs are stored, diagnose each DTC according the
the following priority:
| • | PCM Error DTCs (P0601, P0602). |
| • | System Voltage (P0560, P1635, P1639). |
| • | Component Level DTCs (Switches, sensor range/performance, sensor
high voltage, sensor low voltage, ODMs, etc....). |
| • | System level DTCs (Fuel trim, Misfire, EGR flow, TWC System, Idle
Control System, HO2S Response or HO2S Transition Time Ratio). |
-
A scan tool
parameter which is not within the typical range may help to isolate the area
which is causing the problem.
Powertrain On-Board Diagnostic (OBD) System Check
Step
| Action
| Value(s)
| Yes
| No
|
1
|
- Ignition ON, engine OFF.
- Observe the Malfunction Indicator Lamp (MIL).
Is the MIL ON?
| --
|
Go to Step 2
| Go to
Malfunction Indicator Lamp (MIL) Inoperative
|
2
|
- Ignition OFF.
- Install a scan tool.
- Ignition ON.
- Attempt to display PCM data with the scan tool.
Does the scan tool display PCM data?
| --
|
Go to Step 3
| Go to
Data Link Connector Diagnosis
|
3
| Attempt to start the engine.
Did the engine start and continue to run?
| --
|
Go to Step 4
| Go to
Engine Cranks but Does Not Run
|
4
| Display DTC Info Last Tst Fail. If any DTCs are stored
as last test failed, save the freeze frame and fail record information using
the Capture Info feature on the scan tool.
Are any DTCs indicated as last test failed?
| --
| Go to applicable DTC table
|
Go to Step 5
|
5
| Display DTC Fail Records with the scan tool. If any DTC
Fail Records are stored, save the freeze frame and fail record information
using the Capture Info feature on the scan tool.
Are any Fail Records stored?
| --
| Go
to applicable DTC table
|
Go to Step 6
|
6
| Compare PCM data values displayed on the scan tool to the
typical engine scan data values.
Are the displayed values normal or close to the typical values?
| --
| No trouble found
| Refer to indicated Component System
Checks
|
