Central Control Module (CCM)

Circuit Description

The PASS-Key(R) detection circuit is completed by the PASS-Key(R) (with embedded resistor pellet) in the ignition lock cylinder. Contacts in the ignition lock cylinder mate with those on the pellet, and the CCM compares the resistance value of the key pellet to the "valid" resistance programmed into the CCM at vehicle assembly.

Code 51 will set if, when the ignition is turned "ON," the key pellet resistance does not match the "valid" resistance in the CCM. The code displayed will be history only (H51) unless the faulty key is in the ignition during diagnostics.

Test Description

Number(s) below refer to circled number(s) on the diagnostic chart.

1. This test determines if the key itself is at fault.
2. This test uses the PASS-Key(R) Interrogator test device to determine the key code number, based on its resistance value. Then, the CCM's diagnostic function is used to read the key through the PASS-Key(R) circuit. The CCM-generated value from the odometer display is compared to a chart of CCM values vs. the corresponding key code number. The key code number from the PASS-Key(R) Interrogator is compared to the code number from the chart to see if they match.
3. If the key codes determined in Test 2 do not match, this test checks to see if PASS-Key(R) Codes 52 (short circuit) or 53 (open circuit) are set; the conditions that set these codes could cause the CCM to decide that a good key is actually faulty.
4. This test checks to see if CKT 1073 and its connectors are good up to the ignition lock cylinder connector.
5. This test checks to see if CKT 1074 is open.
6. This test checks to see if the CCM is putting out the desired signal from pin E12.

Diagnostic Aids

Check for poor connections at both the CCM and the ignition lock cylinder assembly; these could cause an open, incorrect PASS~Key� resistance, or intermittent fault. If the code is a history code, the problem may be intermittent. Try performing the tests shown while "wiggling" wiring, connectors, and the key; this can often cause the fault to appear. Refer to "Intermittents/H istory Codes/Poor Connections".

While very unlikely, it is possible that extremely hot or cold ambient conditions may cause a Code 51. To eliminate this possibility, make sure both the vehicle and especially the key are near normal "room temperature" conditions when testing.

Make sure the key resistor contacts are clean and free of any grease, oil, etc. These substances could interfere with the key detection circuit and set a code.

If the key resistor pellet is incorrect there will be no outputs from the CCM to the Starter Enable Relay or the ECM. This state will last approximately 3 minutes. If a key is inserted or the ignition is turned "ON" again before the 3 minute time frame is complete, the timer will reset to 3 minutes. Disconnecting the battery will not clear the timer sequence; it will reset to 3 minutes when battery power is restored. Even if a proper key is inserted during one of the timer periods, the vehicle will not start until the total time period has lapsed.