1998 Buick Century


Transmission problem
1998 Buick Century 6 cyl Two Wheel Drive Automatic 109118 miles

The "service engine soon" light came on, on my 98 buick century engine 3.1, took it to the mechanic he did a diagnostic and code P1870 came on, it has to do something with the transmission, I feel the car is running fine. Mechanic said it could mean anything as small as a change of transmission oil to something more serious. Does anyone have any idea what the problem might be?

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Monday, November 24th, 2008 AT 8:29 PM

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1. Ensure transaxle fluid level is correct. Connect scan tool to DLC. Turn ignition switch to ON position. DO NOT start engine. Using scan tool, record freeze frame and failure records for reference. Data will be lost when DTCs are cleared later in this test. 2. Select "TCC slip speed" on scan tool. With gear selector in "D" position, drive vehicle and ensure TCC is engaged. If TCC slip speed is more than 200 RPM, go to next step. If TCC slip speed is not more than 200 RPM, see DIAGNOSTIC AIDS. 3. Inspect and replace vacuum modulator as necessary. See HYDRAULIC PRESSURE TESTS in AUTO TRANS OVERHAUL section. If modulator is okay, inspect mechanical components and repair or replace as necessary. 4. Check for stuck TCC solenoid or TCC PWM solenoid check ball. Check for stuck converter clutch or regulator valve. Check for cut or missing turbine shaft "O" ring seal. Check for stuck torque converter pressure plate. Check for worn or glazed fiber material in torque converter. Check for stuck 3-4 shift valve. 5. Check for burned or damaged 2nd, 3rd or 4th clutch composition plates. Check for cut or rolled input shaft, 2nd, 3rd or 4th clutch piston seals. Check for rolled or twisted driven sprocket support ring, or worn sleeve in 2nd clutch housing. 6. After repair is complete, select DTC on scan tool. Select "Clear Info" function. Select "Specific DTC" and enter DTC "P1870". Operate vehicle under the following conditions: throttle position is 14-50 percent, engine is not in fuel shut off mode, transaxle range is "D", transaxle is not in 1st gear, MAP is 3-9 psi (20-64 kPa), engine speed is 800-1500 RPM, vehicle speed is 25-75 MPH, speed ratio is.76-.89, PCM commands TCC on for more than 4 seconds, and TCC slip speed is -20 to 30 RPM for more than 5 seconds. If DTC P1870 is not present, repair is complete. If DTC P1870 is still present, repeat test.

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Monday, November 24th, 2008 AT 8:38 PM

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