Accessing and Reading Diagnostic Trouble Codes

In the Diagnostic Mode, the BCM displays any Diagnostic Trouble Codes (DTCs) stored in memory. The DTCs are displayed as flash codes through the "Security" indicator lamp on the Instrument Cluster. During normal operation, if the BCM detects a fault in a monitored system, there is no flash code to indicate to the customer that a fault has occurred, though he/she may detect a system malfunction. System faults are stored by the BCM as "Current", or "History" DTCs. A "Current" DTC means that the fault was present when the Diagnostic Mode was entered. A "History" DTC means the fault occurred sometime after the BCM was installed in the vehicle (or since the last time the DTCs were cleared), but may not currently be present. If a "Current" DTC is stored, the associated "History" DTC will always be stored. When working on systems controlled by the BCM, the technician should always refer to this Section and check for DTCs.

Diagnostics is entered by performing the following steps:

^ Turn the Ignition Switch to the "RUN" position to disarm the Universal Theft Deterrent system, if equipped.

^ Turn the Ignition Switch to the "OFF" position.

^ Remove the RADIO fuse 17 from the I/P fuse block.

^ Turn the Ignition Switch to the "ACC" position (enters Program Mode for feature customization, 1 or 2 Audible Warning tones for mode verification).

^ Within 5 seconds, turn the Ignition Switch to "OFF" and immediately (within 1 second) back to the "ACC" position (enter Diagnostic Mode, 3 Audible Warning tones for mode verification).

The BCM will begin to flash DTCs 4 seconds after entering the Diagnostic Mode. Each flash of the "Security" indicator lamp on the I/P represents a number. For example, one flash followed by two quick flashes represents a code 12. Each code is displayed 3 times before the next code is displayed. Stored DTCs are displayed in numerical order. Once the last code is displayed, the list begins over again with the first code. The display continues until the Diagnostic Mode is exited.

While in the Diagnostic Mode, a transition of certain BCM inputs from active to inactive, or vice versa, will cause the BCM to respond to the transition. For example, if a Door Lock Switch is depressed, the BCM will flash the "Fasten Seatbelt" Indicator Lamp and sound a single audible warning tone. The BCM will also respond in the same way if the hatch or either door is opened or closed, due to the transition at the Door Jamb Switch or the Rear Compartment Lid Ajar Indicator Switch input. In all cases, the BCM will also attempt to perform the operation normally performed by the switch transition.

The BCM will also respond to a change at either the Shock Sensor Tamper Input or the Shock Sensor Shock Input. The Tamper Input is activated by minor blows to the vehicle. The Shock Input is activated by heavy blows. In the Diagnostic Mode, if either the Tamper or Shock Input becomes active due to a blow to the vehicle (or by tapping on the exposed Shock Sensor), the BCM will activate the Horn Relay and cause the horns to chirp. The BCM will also flash the "Fasten Seatbelt" Indicator Lamp and sound an audible warning tone.

Finally, any transition at the Interior Lamps Command Input (switching the Interior Lamps Switch "ON" or "OFF") while in the Diagnostic Mode, will cause the BCM to flash the "Fasten Seatbelt" Indicator Lamp, sound an audible warning tone, and flash the Courtesy Lamps. On vehicles equipped with Universal Theft Deterrent, each transition at the Interior Lamps Command Input will also cause the BCM to step through the actions in the following table:

Step Operation

1 Courtesy Lamps Flash

2 Horns Chirp

3 Exterior Lights Flash