1997 Cadillac Catera 6 cyl Two Wheel Drive Automatic 77000 miles
Transmission goes into limp mode intermittently for the past year. Sometimes several times a day and sometimes not for several weeks. I purchased the car from my dad (low milles) but for the last year since I owned it drive it every day. If the transmission light goes on when I stop I turn the car off and back on and Im on my way. Besides going into the limp mode, getting codes P1700 and P1870 and the Service Engine light turning on I have not felt or heard anything that would make me think there was an issue with the trans. I changed the trans filter and fluid which looked good. Also changed the alternator. Cleared codes or drive serveral trips and the Service Engine light goes out.
DTC P1700 - MIL REQUESTED BY TCM
This DTC indicates that a transmission related OBD-II failure has occurred. Transmission Control Module (TCM) controls a dedicated service transmission light, which is illuminated when a failure is reported by certain non-emission related TCM diagnostics. TCM has no direct control of engine MIL, but if transmission fault occurs that is emission related, MIL must illuminate. A MIL request circuit between ECM and TCM provides a means for illuminating MIL, even though fault was detected by TCM. This circuit is increased to battery voltage within ECM. To illuminate MIL, TCM lowers circuit voltage. ECM detects this and DTC is set, which illuminates MIL.
Condition required to set DTC is: Ã
An OBD-II transmission DTC has been stored by TCM.
Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. If OBD system check was performed previously, diagnose transmission malfunction.
DTC P1870: TORQUE CONVERTER CLUTCH (TCC) STUCK OFF
TCM can calculate speed of turbine in torque converter by using engine speed, output speed and gear. If TCC solenoid DTC is not set, and TCM detects a slippage of more than a specific amount with TCC commanded on, TCM concludes that TCC is stuck off (not engaged). DTC P1870 will set if TCM detects a slippage between engine speed and turbine speed.
Conditions For Setting DTC P1870
DTC will set under the following condition: Ã
Absolute slippage between engine speed and calculated turbine speed is more than 288 RPM.
Action Taken By TCM
TCM performs the following if DTC is set: Ã
Transmission operates in default mode.
ECM records operating conditions in freeze frame at time of MIL request from TCM.
TCM illuminates transmission light and sends a MIL request to ECM on second consecutive ignition cycle that diagnostic runs and fails. ECM then illuminates MIL.
If DTCs P0730 or P0743 are also set, diagnose these DTCs first. If DTCs are not present, diagnose internal transmission malfunction.
Problem is caused by intermittent failure of the TCC and diagnostics would be required to locate the source.