A shop recently had a car come in with the ABS light on and a code for the lateral accelerometer and yaw sensor module or cluster. The that indicated the ABS HCU and PCM where unable to communicate with the lateral+longitudinal accelerometer and yaw sensor cluster. The owner was freaked out when the dealer told him that it would cost $620 for the sensor cluster.The first step was to clear the code and go for a test drive with the scanner. It is one thing look at a scan tool for engine data when cruising or accelerating. It is very difficult and even dangerous to drive the vehicle and look at the readings from an accelerometer. Chances are you will see only minor movement in the sensor data. The technician went into a empty parking lot and started to do circle to look at the data on the scan tool.
As he started to do circles in the parking lot, a little old lady called to police to complain about someone doing donuts in a parking lot. The police showed up and the tech was commended on not testing on the road, but was told to move on.
Lateral+longitudinal accelerometers and yaw sensors measure braking and acceleration force in G-Force. they are mounted in the center of the vehicle at the center of gravity. This is typically in the center console, under the cup holders. The technician’s data was inclusive because he could not tell a tug on the steering wheel from a short in the sensor.
The best tests are against a “known value.” You can check resistance through a circuit, you can compare a fuel sample against a fresh fuel. To test accelerometers you have the best “known value” on the planet, it is the planet’s constant 1-g of gravity that is keeping you from floating into space.
To measure the performance of an accelerometer is to rotate it 90 degrees. When a lateral accelerometer is rotated 90º, it should read 1-G. When a longitudinal sensor is rotated on its end, it will read 1-G. This is because gravity is equal to 1-G. Since it is impossible to rotate a car 90 degrees on a lift (Don’t even try), pull the console and unbolt the sensor. You can check the performance on a scan tool or scope.
Most accelerometers are wired with three wires. These include a 5-volt power, ground and signal wires. The signal wire will vary the voltage from 0-5-volts depending on G-force.
So what was the problem? When the console was pulled there was an accumulation of coffee, cola and unidentified liquids in the area of the sensor cluster. The sensor was functioning but not communicating with the vehicle due sugar and latte shorting out two high-speed CAN wires. Once the connection was cleaned and the codes were cleared, the vehicle was back to normal.
