SPORADIC ENGAGEMENT OF THE TORQUE CONVERTER CLUTCH

MODELS AFFECTED: 1988 CIMARRONS

Some 1988 Cimarrons equipped with a mechanical instrument cluster may experience sporadic engagement and disengagement of the Torque Converter Clutch (TCC) which may also be described as a surge or chuggle in the 32-40 mph range. This condition may be caused by a bent or kinked speedometer cable. The cable from the transmission to the cluster drives the speedometer needle. The signal from the cable is buffered in the cluster and then sent to the ECM. The ECM has certain fixed values for minimum TCC lock and unlock speeds which center around 32-40 mph.

If the speedometer cable is kinked or bent, an inconsistent speed signal will be passed through the buffer and sent to the ECM. The ECM will interpret the varied speed signal as actual vehicle speed changes. If a variation in speed signals occurs at 32-40 mph, the correct criteria may be met in the ECM such that the ECM would command the TCC to lock and unlock.

To diagnose this condition:

1. Determine if the speedometer needle flutters. If it does, then check the cable routing for kinks or bends and replace if necessary.

2. If the speedometer needle does not flutter, hook up a scan tool and monitor the TCC enable/disable status light during the condition.

A. If the staws light is indicating that the ECM is enabling and disabling the TCC, then monitor the following inputs to the ECM to determine which input is telling the ECM to engage and disengage the torque converter clutch. These inputs should remain steady while the Torque Converter Clutch is engaged:

o VSS o TPS o Brake Switch should remain closed o Third Gear Switch should remain closed o O2 Sensor should remain in closed loop

If any of these inputs do not remain steady, refer to Section 6E3 of the 1988 Cimarron Service Information Manual for diagnostic procedure.

B. If the TCC status light remains on or remains off during the condition, refer to the 1988 Cimarron Service Information Manual, Section 6E, Subsection B under "Surges and/or Chuggle" for additional information.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.