Circuit Description
The provision for communicating with the control module is the data link connector (DLC). The DLC is usually located under the instrument panel. The DLC is used to connect to a scan tool. Some common uses of the scan tool are listed below:
| • | Identifying stored diagnostic trouble codes (DTCs) |
| • | Clearing DTCs |
| • | Performing output control tests |
| • | Reading serial data |
Battery power and ground is supplied for the scan tool through the DLC. The Class 2 serial data circuit to the DLC allows the PCM to communicate with the scan tool. The Class 2 serial data circuit is also used to communicate with the electronic brake control module (EBCM).
Diagnostic Aids
Ensure that the correct application--the model year, the car line, and the VIN code--has been selected on the scan tool. If communication still cannot be established, try the scan tool on another vehicle to ensure that the scan tool or the cables are not the cause of the condition.
An intermittent may be caused by the following:
| • | Poor connection |
| • | Rubbed-through wire insulation |
| • | Broken wire inside the insulation |
Any circuitry that is suspected of causing an intermittent complaint should be thoroughly checked for the following conditions:
| • | Backed-out terminals |
| • | Improper mating of terminals |
| • | Broken locks |
| • | Improperly formed or damaged terminals |
| • | Poor terminal-to-wiring connections |
| • | Physical damage to the wiring harness |
| • | Corrosion |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
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The Powertrain OBD System Check prompts the technician to complete some basic checks and store the Freeze Frame Data and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. This information on the scan tool can be referred to later.
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If the scan tool requires an external power supply, check the external supply for proper voltage and ground as well as the voltage and ground supplies in the DLC.
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Locate and repair any shorts that may have caused the fuse to open before replacement, if the no voltage conditions due to an open fuse.
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Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be performed. Refer to the latest Isuzu Technical Communication System (ITCS) information for programming procedures and also refer to the Powertrain Control Module (PCM) .
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The scan tool, or associated cables could be faulty. Refer to the scan tools manual for repair information.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | |||
Important: Go to Step 3 if the scan tool uses an external power supply, refer to the test description. Does the scan tool power up? | -- | |||
3 | Attempt to communicate with the other modules with the scan tool. Does the scan tool communicate with the other modules? | -- | ||
4 |
Does the scan tool communicate with the other modules? | -- | ||
5 | With the test light connected to ground, probe the specified DLC battery feed circuit terminal. Does the test light illuminate? | 16 | ||
6 | With the test light connected to B+, probe the specified DLC ground circuit terminals. Does the test light illuminate for both circuits? | 4,5 | ||
Repair the open or short to ground in the DLC battery feed circuit. Is the action complete? | -- | -- | ||
8 | Check the DLC electrical terminals for proper tension or excessive resistance and repair as necessary. Was repair necessary? | -- | ||
9 | Repair open or poor connection(s) in the DLC ground circuit(s). Is the action complete | -- | -- | |
10 | Check for an open in the Class 2 serial data line from the splice to the PCM. Repair if circuit or connections are found malfunctioning. Was a malfunction found? | -- | ||
11 | Check for a short or open in the Class 2 serial data line from the DLC to the PCM. Repair if circuit or connections are found malfunctioning. Was a malfunction found? | -- | ||
Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
13 | Install the scan tool on another vehicle with Class 2 serial data and check for proper operation. Does the scan tool work properly on a different vehicle? | -- | Go to section 8A | |
Is the action complete? | -- | -- | ||
15 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
16 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to Applicable DTC Table | System OK |
