I have a 00 sunfire 2.2l 3spd auto. I am getting a CEL for p1870. first of all trying to clear up what it means because I have visited three different web sites and each one says something different, in general i have found it is something wrong with the trans. The previous owner had it looked at and his mechanic said it was a torque converter clutch solenoid. and it'd be $300 to get it fixed. does this make sense for the code it is throwing. the car runs and drives.

the computer is looking for the rpm drop when the tcc ciruit is commanded by the pcm.if it does not see that it will illuminate the light after two failures. tcc solenoid ,wiring,pcm or internal trans part possible. needs diagnostics to identify exact cause

My TCC is working not currently, but when it was, I got this code after cruising in variable speed traffic. Mine was tripped by the disparity of the engine rpm and the speed, i.e. due to the fact I swapped the final drive from the stock 2.84 differential (3.18 effective w/ 33/37 drive gears) to the 3.08 differential (3.43 effective w/ 33/37 drive gears). The PCM saw the difference of the rpm the was turning and the actual speed i was going, from the speed sensor on the transmission's output at the differential. With the lower gearing, I was turning more rpm than the PCM was programed for at a particular speed. Being outside the speed parameters programed, the PCM tripped the code as if the TCC is bad.

From GM's service information:

Circuit Description
The powertrain control module (PCM) monitors the torque converter clutch (TCC) slip speed. The PCM calculates the difference between the engine speed and the transmission output speed. In D3 drive range with the TCC engaged, the engine speed should closely match the transmission output speed.

When the PCM detects excessive slip of the TCC, the forward clutch, and the direct clutch when the TCC is engaged in 3rd gear, then DTC P1870 sets. DTC P1870 is a type B DTC.

Conditions for Running the DTC
• No Throttle Position (TP) sensor DTCs P0121, P0122 or P0123.
• No Vehicle Speed Sensor DTCs P0502 or P0503.
• The engine speed is 1,500-3,600 RPM.
• Engine torque is greater than 27 N·m (20 lb ft).
• The throttle angle is 10-40 percent.
• The torque converter clutch (TCC) is on for 5 seconds.
• The TCC slip speed is greater than 140 RPM for 8 seconds.
• The vehicle speed is 56-120 km/h (35-75 mph).
• The speed ratio is 0.90-1.375.

Conditions for Setting the DTC
The PCM transmission slip counter is greater or equal to one count.

Action Taken When the DTC Sets
• The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the conditions for setting the DTC are met.
• The PCM inhibits TCC engagement.
• The PCM stores DTC P1870 in PCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.

Conditions for Clearing the MIL/DTC
• The PCM turns off the MIL during the third consecutive trip in which the diagnostic test runs and passes.
• A scan tool can clear the MIL/DTC.
• The PCM clears the DTC from PCM history if the vehicle completes 40 consecutive warm-up cycles without an emission-related diagnostic fault occurring.
• The PCM cancels the DTC default actions when the fault no longer exists and/or the ignition is off long enough in order to power down the PCM.

Diagnostic Aids
• Inspect the connectors at the PCM, AT inline harness connector and all other circuit connecting points for an intermittent condition. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
• Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical Intermittents in Wiring Systems.
• Verify that the final drive ratio is correct for the vehicle.
• Check for overloading or trailer towing in excess of vehicle capacity.


Low fluid level may be causing the slipping.
Low line pressure may be causing the slipping.

John Lenko wrote:From GM's service information:

Circuit Description
The powertrain control module (PCM) monitors the torque converter clutch (TCC) slip speed. The PCM calculates the difference between the engine speed and the transmission output speed. In D3 drive range with the TCC engaged, the engine speed should closely match the transmission output speed.

When the PCM detects excessive slip of the TCC, the forward clutch, and the direct clutch when the TCC is engaged in 3rd gear, then DTC P1870 sets. DTC P1870 is a type B DTC.

Conditions for Running the DTC
• The engine speed is 1,500-3,600 RPM.
• Engine torque is greater than 27 N·m (20 lb ft).
• The throttle angle is 10-40 percent.
• The torque converter clutch (TCC) is on for 5 seconds.
• The TCC slip speed is greater than 140 RPM for 8 seconds.
• The vehicle speed is 56-120 km/h (35-75 mph).
• The speed ratio is 0.90-1.375.

Conditions for Setting the DTC
The PCM transmission slip counter is greater or equal to one count.

Diagnostic Aids
• Verify that the final drive ratio is correct for the vehicle.

Exactly what happens with mine, just now described in the service manual.

Thank-you John.