See Figures 1 through 26
Diagnosis of a driveability problem requires attention to detail and following the diagnostic procedures in the correct order. Resist the temptation to begin extensive testing before completing the preliminary diagnostic steps. The preliminary or visual inspection must be completed in detail before diagnosis begins. In many cases this will shorten diagnostic time and often cure the problem without electronic testing.
This is possibly the most critical step of diagnosis. Many fault codes or apparent failures are caused by loose, damaged or corroded electrical connectors. A detailed examination of all connectors, wiring and vacuum hoses can often lead to a repair without further diagnosis. Performance of this step relies on the skill of the technician performing it; a careful inspector will check the undersides of hoses as well as the integrity of hard-to-reach hoses blocked by the air cleaner or other components. Wiring should be checked carefully for any sign of strain , burning, crimping or terminal pull-out from a connector.
Checking connectors at components or in harnesses is required; usually, pushing them together will reveal a loose fit. Pay particular attention to ground circuits, making sure they are not loose or corroded. Remember to inspect connectors and hose fittings at components not mounted on the engine, such as the evaporative canister or relays mounted on the fender aprons. Any component or wiring in the vicinity of a fluid leak or spillage should be given extra attention during inspection.
Additionally, inspect maintenance items such as belt condition and tension, battery charge and condition and the radiator cap carefully. Any of these very simple items may affect the system enough to set a fault. The self-diagnostic system will not operate if the battery is low on charge.
READING FAULT CODES
All stored codes are read through connections at the diagnostic connector. The DRB-II or equivalent may be used to read stored codes; the Mitsubishi Adapter must be used as an interface between the scan tool and the vehicle. The DRB-II may be used to read codes and observe the signal values being sent to and from the ECU. Fault codes stored within the system may be cleared through the DRB-II.
In the absence of a scan tool and/or adapter, codes may be read directly from the diagnostic connector. All stored fault codes are read through an analog (needle type) voltmeter after the system enters self-diagnostics. The codes are transmitted as pulses which cause the needle to sweep repeatedly. To enter the self-diagnostic mode:
- The self-diagnostic connector is located either next to or below the fuse panel, under the left dash. The only exception is the Colt Wagon, which locates the connector under the left side of the glove box, behind the center console. Remove the cover if one is fitted.
- With the ignition switch OFF , connect the ground probe of the voltmeter to the ground terminal (terminal No. 12) of the diagnostic connector.
- Connect the voltage probe of the voltmeter to the MPI diagnostic terminal (terminal No. 1) of the connector.
- Turn the ignition switch ON but do not start the engine. The codes will be transmitted immediately. Each two-digit code will be sent as groups of electrical pulses; these pulses will cause needle sweeps on the voltmeter. The codes are sent in place value groups. For example, Code 23 is sent as a group of 2 long pulses followed by a group of 3 shorter pulses. There is a short pause between place value groups and a longer pause between code groups.
If multiple codes are stored in the memory they will be transmitted in numerical order from lowest to highest, not in the order of occurrence.
- If the ECU detects an internal error, the needle on the voltmeter will show constant voltage instead of sweeping on and off. When this signal is received, the ECU must be replaced.
- If no faults are stored within the memory, the Normal State signal will be displayed. This is a constant, rapid needle sweep with no pauses or groups. This signal shows that the system understands the request for stored data but has nothing to report.
- Record the codes transmitted for use during repairs. Once the codes are recorded, switch the ignition OFF . Based on the codes, perform diagnostic and test procedures on the individual components and circuits.
If, during testing or repair, a sensor is disconnected with the ignition ON, the fault code for that sensor or circuit will be set. For this reason, having the original codes written down will eliminate confusion about additional codes appearing during testing or repair.
CLEARING STORED CODES
After all diagnosis has been completed and the needed repairs performed, the stored fault codes must be erased from the ECU memory.
Codes may be cleared using the DRB-II. When properly connected through the Mitubishi Adapter, select ADJUSTMENTS from the Main Menu screen. Choose item 1, ERASE FAULTS and follow the directions given on the screen.
Alternately, with the ignition switch OFF , disconnect the negative battery terminal for at least 10 seconds. This will also clear the stored codes. When the battery is reconnected, double check the repair by road testing over a moderate distance, then checking for newly-set codes.