DTC Capabilities

DTC Capabilities
The Instrument Cluster is capable of storing diagnostic trouble codes (DTC) and will communicate with the DRBIII to display codes. The cluster has the ability to set DTCs for internal cluster failure, lack of communication with other modules, Air Bag Lamp circuit failure, and Panel Dimmer circuit failure.

If the cluster failure is a gauge or meter concern, DTCs will be stored by the PCM. Because the Instrument Cluster receives gauge and meter information from the PCM over the PCI Bus, it is the PCM's function to monitor these inputs and to store DTCs. For this reason the PCM DTCs should be checked first for any condition regarding a gauge problem, except for the Oil Pressure gauge.

There are DTCs associated with all the gauges except for the Oil Pressure gauge. The cluster receives oil pressure information from the PCM over the PCI Bus, but the PCM does not create DTCs for any oil pressure concerns. When diagnosing a gauge concern, 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 is the same information used by the PCM to generate the PCI Bus gauge messages. OBD II requirements state that the fuel level sender must be checked for rationality. This includes determining if the fuel 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 DTC. The presence or absence of a fuel level sending code in the PCM is an important factor to determine whether a fuel gauge problem is in the sending unit or in 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 verification of oil pressure readings.