Reading Diagnostic Trouble Codes

STORED FAULTS

The Engine Controller has been programmed to monitor many different circuits of the fuel injection system. If a problem is sensed in a monitored circuit often enough to indicate an actual problem, a fault is stored. It will be stored in the Engine Controller memory for eventual display to the service technician. If the problem is repaired or ceases to exist, the Engine Controller cancels the fault after 51 engine starts.

FAULT CRITERIA

Certain criteria must be met for a fault to be entered into Engine Controller memory. The criteria may be a specific range of engine rpm, engine temperature, and/or input voltage to the Engine Controller.

It is possible that a fault for a monitored circuit may not be entered into memory even though a malfunction has occurred. This may happen because one of the fault criteria for the circuit has not been met. Example: assume that one of the criteria for MAP sensor circuit is that engine must be operating between 750 and 2000 rpm to be monitored for a fault. If the MAP sensor output circuit shorts to ground when engine rpm is above 2400 rpm, a 0 volt input will be seen by the Engine Controller. A fault will not be entered into memory because the condition does not occur within the specified rpm range.

OPERATING CONDITIONS

There are several operating conditions that the Engine Controller does not monitor and set faults for. Refer to Monitored Circuits and Non-Monitored Circuits in this section.

EXTRACTING FAULTS

Stored fault codes can be displayed by cycling the ignition key ON - OFF - ON - OFF - ON. They can also be displayed through use of a Diagnostic Scan Tool. The Scan Tool connects to the diagnostic connector in the vehicle.