Instruments - Description & Operation: Description: Diagnostics: Notes

The instrument pack provides an interface (gateway) for data transfer between T4 and the vehicle ECU's. Individual ECU's subject their functional capabilities to self diagnostic checks. Any irregularities or malfunctions are stored in the ECU error memory. The error memories can be interrogated by T4 to establish and diagnose the cause of the error messages.

The instrument pack RAM can be reset with T4 or using the instrument pack test No. 21 (see Instrument Pack Test ). When this procedure is performed, all values stored in the RAM will be erased. Displayed values to the driver, such as trip meter reading and on-board computer sequence and values, will be erased and resume their default values or are reset to values of zero.

The instrument pack also performs a self diagnostic routine to check its function and monitoring of related components. Detected errors are written to the RAM initially and then transferred to the EEPROM when the ignition is switched off. The EEPROM will only store the five most recent errors. If five errors are stored, only further errors of the bus systems or instrument pack EEPROM errors will be memorized in their order of occurrence. Errors already present will be over written. Error messages can be retrieved and diagnosed with T4. When the instrument pack is reset, errors stored in the EEPROM are transferred to the RAM and then erased.