Diagnostics

GAUGES
The instrument cluster will not store any DTCs. Because the engine controller gathers all the gauge information and sends it to the cluster via the bus, it is the PCM's responsibility to monitor these inputs and store DTC's for them, For this reason the first item to be checked regarding a gauge problem (except oil pressure) should be the PCM for any DTCs relating to the gauge in question.

There are DTCs associated with all the gauges except for the oil pressure gauge. When diagnosing gauges, the input that is used for the gauge message (fuel level sender for example) must be valid. Because of OBD II requirements, most of the information used for monitoring the OBD II system happens to be the same information used by the PCM to formulate the gauge bus messages. OBD II requirements state that the fuel level sender must be checked for rationality. This includes determining if the sending unit voltage is too high or too low or if the voltage hasn't changed over time. If the PCM has determined that the sender information isn't valid, it will set a diagnostic trouble code. The presence or absence of the fuel level sending code in the PCM is an important factor to determine whether a fuel gauge problem is in the sending unit or the cluster.

This same situation is used in all cluster diagnostics related to gauge operation with the exception of the oil pressure gauge. OBD II requirements do not include oil pressure monitoring. Therefore, oil pressure diagnostics would dictate that a mechanical oil pressure gauge be attached to the engine for absolute verification of oil pressure readings.

HARDWIRED LAMPS
The cluster contains several hardwired lamps described earlier. These lamps are set up in two configurations. Either the lamp is supplied power by the cluster and the ground is supplied by the circuit being monitored or the lamp is supplied by the ground in the cluster and power comes from a module or other device. Refer to the schematic for the specific details on the lamp in question. Verification of the bulb filament may be required in all cases of an inoperative lamp. This will require removal of the cluster and the bulb in question.

CCD CONTROLLED LAMPS
The cluster contains several CCD controlled lamps as described earlier. These lamps are part of the diagnostic self-test. When entering the self-test mode, operation of these lamps can be observed. If the bulb fails to operate during the self-test and the bulb filament is good, the cluster assembly will need to be replaced.