Intermittents/History DTCs

History DTCs are those indicating that the CCM previously detected a fault which later disappeared. Any DTC that has a 1 as its first digit is a history DTC. Examples are: 120, 132, 137 etc. The reason could be either that the fault is a true intermittent, only happening occasionally, or that the system for which the DTC is not currently being operated. An example of this would be DTC 143 (key resistor circuit short to battery/open) CKT 1073 could have an intermittent short to B+. For this reason, if a DTC and operating the system that the DTC applies to. If the DTC resets, it can be assumed that the condition is present.

If a visual (physical) check does not find the cause of the problem, the vehicle can be driven with a DVM connected to the suspected circuit. An abnormal voltage or resistance reading when the problem occurs indicates the problem may be in that circuit.

In the case of the circuits which can be monitored by using the Tech 1 data display, these may be monitored for abnormal voltage, counts, etc. which occur at the same time the problem occurs, possibly indicating a problem with that circuit.

One example of this is DTC 22 changing from DTC 22 to DTC 122 while you are watching the Heater-A/C Control display. An intermittent short to B+ in CKT 1393 could cause the diagnostic display to alternate between DTC 22 and DTC 122. All History DTCs will clear if there has been no faults for 50 ignition cycles. For more information on intermittents and troubleshooting, refer to DIAGRAMS.