1997 STS

[CUNYSTEVE]

I GOT THE MESSAGE AND CHECKED THE CODE ( TC 1285) AND THE CODE GIVES THE DISCRIPTION LATERAL ACCELEROMETER SENSOR CIRCUIT MALFUNCTION. DOES ANYONE KNOW WHAT THAT MEANS, WHAT HAS TO BE DONE TO FIX IT, AND HOW MUCH THAT MIGHT COST?

[Cadillac Jim]

The lateral accelerometer is under the passenger seat, bolted on the rear of the fornt of the two raisl under the the seats. See Figure 15, page 5E2-220. The connector is a three-wire waterproof latched jack that plugs into the sensor from the left (passenger) side.

This is from the 1997 FSM pages 5E2-172 through 176.

The lateral accelerometer connects to the EBTCM with three wires: 5 Volts from a gray/black wire, ground from a green/black wire, and the accelerometer signal throough a light blue wire. The 5 Volts and ground are shared with the yaw rate sensor, which is behind the rear seat on the bottom of the parcel shelf and is accessed throug the trunk.

The output voltage on the light blue wire must be between 0.25 Votls and 4.75 Volts. Zero acceleration is 2.5 Volts. DTC C1285 is set when the signal is less than 0.15 Volts or greater than 4.85 Volts for 1 second or more. The DTC will remain set until it is manually cleared, or you start the car 50 times.

If you noticed exactly when the STABILITY REDUCED message appeared, think about what the car was doing at that moment when you try to understand what caused the problem.

The first thing to do is to look at the wiring. Something under the passenger seat could hang on the seat and wiring and push the connector away from the sensor when the electric seat is moved in any direction, particularly down or back. Also, I once saw this code flash when I had a battery cable problem. A bad battery or cable can cause this code to flash when you are starting the car, or when you hit a bump.

You can check the wires between the EBTCM and the lateral accelerometer for damage or shorts by disconnecting it on both ends and using an ohmmeter. The A (5 Volt supply, gray/black) wire on the lateral accelerometer connects to terminal 11 on the EBTCM connector, the B (output, light blue) wire on the lateral accelerometer connects to pin 22 of the EBTCM connector, and the C (sensor ground, green/black) wire on the lateral accelerometer connects to pin 27 on the EBTCM connector. Make sure that none of them are shorted to ground or each other, and that you have continuity from the EBTCM to the lateral accelerometer on each of them. Note that the signal ground wire is not a ground and should not be shorted to ground.

A sort on the 5 Volt or ground line can be in the cable to the lateral accelerometer or to the yaw rate sensor.

When the wiring check is complete, plug everything back in, with a small cheater wire giving you access to the lateral accelerometer 5 Volt supply, sensor ground, and signal, and turn on the ignition and check the accelerometer output voltage. If the 5 Volt supply voltage is between 4.5 Volts and 5.5 Volts, the is signal is between 2.35 Volts and 2.65 Volts, both relative to the sensor ground, you are done, clear the code and drive the car to see if it comes back. If the supply is good but the output is not, replace the sensor.

Replacing the lateral accelerometer (page 5E2-218:

Remove the passenger seat. Don't forget to unplug all the connectors before you lift it out. Pull the trim panel push-in fasteners and pull up the carpet. The later accelerometer mounting screws may (the FSM's word, not mine) be accessible between the front and rear carpet halves. Remove the two screws and pull it out, then remove the connector.

Looking at all this from the DIY perspective, you might as well start by checking the connector under the seat, and pushing it onto the sensor if it seems to be at all out-of-place. Then check the battery cable and, if you have any doubts whatsoever, have the battery load-checked. At that point I would pull the passenger seat and unbolt the sensor. You can check the sensor voltages first with the sensor out, and if it is bad, it is already in your hand. Then, if any of the voltages are bad, do all the wiring checks using long alligator clips on the connector to check continuity of the wires from the EBTCM connector side. If the wiring is good, then the sensor is laying on your workbench ready to take to the dealer for ordering another one. Be sure and have your VIN with you when you order any part from the dealer.