I was driving for a vacation, about 3 1/2 to 4 hours in with the cruise set at about 62-63 my CEL came on. When i got back home from vacation had the code checked at the local advanced auto parts store, they say its P1870, i know this is cause by transmission component slippage, i have checked my fluid, its pretty clean, nice and redish pink colored. but it is a little over full, would that be an issue? o just had all 4 tires put on so thats not the problem. i have read about an aftermarket valve and sleeve that can be replaced in the valve body. does anyone know how long it takes, how much work is needed, and about how much it costs? I'm a diesel mechanic for International so i have mechanical background. also how big of a problem is this? should i not drive the car? i had the code erased and it doesn't want to come back on unless i go for a long drive. and 1-2 upshift is a little rough too.

If your to over full you can foam up the fluid and that can cause some problems. But your saying this only happens on long drives. I would tend to believe your trans is getting over heated, but this is hard to determine unless you have a way of scanning. What year is this car and what is the trim level?

its a 1997, se sedan, with the 3.8 non supercharged 4 speed auto trans, it has roughly 82700 miles

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) monitors the Torque Converter Clutch (TCC) slip by calculating the difference between the engine speed and the transmission output shaft speed. If the PCM detects an excessive amount of slip when the TCC is engaged, then DTC P1870 sets. DTC P1870 is a type B DTC.

CONDITIONS FOR SETTING THE DTC

• No Throttle Position (TP) DTCs P0122 or P0123.
• No Vehicle Speed Sensor (VSS) DTCs P0502 or P0503.
• No 1-2 solenoid performance DTC P0751.
• No 1-2 solenoid electrical DTC P0753.
• No 2-3 solenoid performance DTC P0756.
• No 2-3 solenoid electrical DTC P0758.
• No TCC Pulse Width Modulation (PWM) solenoid electrical DTC P1860.
• No TCC solenoid electrical DTC P0740.
• The engine speed is 800-5000 RPM.
• Not in fuel shut off.
• The throttle angle is 8-35%.
• The transmission is not in first gear.
• The transmission gear range is D4.
• The transmission fluid temperature is 20-130°C (68-266°F).
• The engine torque is 70-230 Nm (50-170 ft lbs.).
• The speed ratio is 0.70-1.05.
• The vehicle speed is 56-120 km/h (35-75 mph).
• The TCC is commanded ON and at maximum apply for 5 seconds.
• The TCC slip is 200-1500 RPM for 8 seconds.
• The above conditions must occur three times with the TCC commanded OFF between each occurrence.

ACTION TAKEN WHEN THE DTC SETS

• The PCM inhibits TCC operation.
• The PCM inhibits 4th gear, if the transmission is in the hot mode.
• The PCM illuminates the Malfunction Indicator Lamp (MIL) after 2 consecutive ignition cycles with a failure reported.

Conditions for Clearing the MIL/DTC

• The PCM turns OFF the MIL after three consecutive ignition cycles without a failure reported.
• A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported.
• The PCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the PCM.

DIAGNOSTIC AIDS

• Ensure that the vehicle'* final drive ratio matches the PCM'* calibration.
• Ensure that the transmission will shift through all four gears with the gear select lever in the D4 range.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic chart.

1. This Step inspects the modulator assembly, which could cause P1870 to set.
2. These are the components that could cause P1870 to set.

Now that we named the code and posted some info about it, let'* talk about it.

The EPC or pressure soleniod is frequently tossing it'* own code, but not a very common code until the 2000 year.

I'd suggest since you mention recently getting new tires that you double check all 4 are the same size via the sidewall. Otherwise..the fsm'* suggest checking the vacuum modulator on the front of the transmission (canister looking thing) and it'* vacuum hose. Beyond that it has you in the transmission.

That in itself isn't horrible if you have some mechanical experience. Lower that side of the subframe to get clearance to remove the sidecover. Then the valves are accessible. FSM'* have a person going through each soleniod and valve to ensure each isn't glazed or bad.

Alright, how should i check the vacuum modulator? is there a check valve in there that i could blow on either end to see if i can blow through or something? if it was one of the solenoids or valves wouldn't i be getting another code thrown too?

Try searching, I don't have much info from my current location. Other soleniods etc should throw their own codes. This one though seems to be for what is listed.

ok, thanks =]