Diagnostics · System playbook

Chassis Control

ABS lights are wheel-speed sensors until proven otherwise.

ABS, traction control, and stability lights come on together because they share the same inputs — and the input that fails is overwhelmingly a wheel-speed sensor or its tone ring. The sensor lives in the worst neighborhood on the car: heat, salt, rust, and suspension movement. Diagnosis is graphing four sensors and finding the liar.

What the symptoms mean

ABS + traction lights on

Wheel-speed sensor or ring — pull codes, then graph all four

ABS activates at low speed on smooth road

Rusty tone ring or metal-packed sensor faking a wheel lockup

Steering angle or stability codes after alignment/battery

Sensor needs recalibration, not replacement

Brake pedal pulsation + ABS noise at every stop

False activation — inspect rings and sensor air gaps

The diagnostic order

Work top to bottom — the order is the point. Each step rules out the cheapest, most common causes before anything expensive gets blamed.

Pull ABS module codes with a capable scanner — the code names the corner and saves the guessing.
Graph all four wheel speeds on a drive: the bad one drops out, reads zero, or gets erratic where the others stay smooth.
At the named corner: pull the sensor, inspect the tip for packed metal, and eyeball the tone ring for rust jacking or cracks (press-on rings on CV shafts split with age).
Measure the sensor per type (resistance for passive; scope or scan data for active) and inspect the harness through its full suspension travel.
After steering-angle work or battery disconnects, run the recalibration before condemning parts.

Tools that matter here

Scan tool with ABS access and graphingMultimeterA lift and a light — half this diagnosis is visual

The classic mistakes

Replacing a sensor when the tone ring is the cracked party — the new sensor reads the same broken ring.
Skipping steering-angle calibration after alignment and blaming the module.
Ignoring wheel bearing play: a loose bearing changes the sensor air gap and fakes sensor codes.

Pro tip: A wheel-speed fault that appears only during turns is a cracked press-on tone ring opening up under shaft flex. Graph it in a parking-lot figure eight and watch the dropout happen live.

Chassis Control trouble codes (79)

C0085Brake Pressure Sensor Circuit C0086Master Cylinder Pressure Sensor Ci…C0087Master Cylinder Pressure Sensor Ci…C0088Brake Fluid Level Sensor Circuit C0089Brake Fluid Level Low C0090Brake Booster Pressure Sensor Circ…C0091Brake Booster Performance C0095Brake Lamp Switch Circuit C0096Brake Lamp Switch Circuit 2 Malfun…C0100Brake Pedal Position Sensor Circui…C0101Brake Pedal Position Sensor Range/…C0105Brake Pedal Position Sensor Circui…C0106Brake Pedal Position Sensor Circui…C0110Brake Apply Circuit C0111Brake Apply Circuit Low C0112Brake Apply Circuit High C0130Brake Pad Wear Sensor Circuit Fron…C0131Brake Pad Wear Sensor Circuit Rear C0135Brake Rotor Temperature Excessive C0140Electronic Brake Force Distributio…C0141EBD Brake Pressure Sensor Correlat…C0145Brake Assist System Malfunction C0146Brake Assist Solenoid Circuit P0008Engine Position System Performance…P0009Engine Position System Performance…P0320Ignition/Distributor Engine Speed …P0321Ignition/Distributor Engine Speed …P0322Ignition/Distributor Engine Speed …P0323Ignition/Distributor Engine Speed …P0335Crankshaft Position Sensor A Circu…P0336Crankshaft Position Sensor A Circu…P0337Crankshaft Position Sensor A Circu…P0338Crankshaft Position Sensor A Circu…P0339Crankshaft Position Sensor A Circu…P0340Camshaft Position Sensor A Circuit…P0341Camshaft Position Sensor A Circuit…P0342Camshaft Position Sensor A Circuit…P0343Camshaft Position Sensor A Circuit…P0344Camshaft Position Sensor A Circuit…P0345Camshaft Position Sensor A Circuit…P0346Camshaft Position Sensor A Circuit…P0347Camshaft Position Sensor A Circuit…P0348Camshaft Position Sensor A Circuit…P0349Camshaft Position Sensor A Circuit…P0365Camshaft Position Sensor B Circuit…P0366Camshaft Position Sensor B Circuit…P0367Camshaft Position Sensor B Circuit…P0368Camshaft Position Sensor B Circuit…P0369Camshaft Position Sensor B Circuit…P0370Timing Reference High Resolution S…P0371Timing Reference High Resolution S…P0372Timing Reference High Resolution S…P0373Timing Reference High Resolution S…P0374Timing Reference High Resolution S…P0375Timing Reference High Resolution S…P0376Timing Reference High Resolution S…P0377Timing Reference High Resolution S…P0378Timing Reference High Resolution S…P0379Timing Reference High Resolution S…P0385Crankshaft Position Sensor B Circu…P0386Crankshaft Position Sensor B Circu…P0387Crankshaft Position Sensor B Circu…P0390Camshaft Position Sensor B Circuit…P0391Camshaft Position Sensor B Circuit…P0392Camshaft Position Sensor B Circuit…P0393Camshaft Position Sensor B Circuit…P0394Camshaft Position Sensor B Circuit…P0395Camshaft Position Sensor B Circuit…P0396Camshaft Position Sensor B Circuit…P0397Camshaft Position Sensor B Circuit…P0398Camshaft Position Sensor B Circuit…P0399Camshaft Position Sensor B Circuit…P0504Brake Switch A/B Correlation P0555Brake Booster Pressure Sensor Circ…P0556Brake Booster Pressure Sensor Circ…P0557Brake Booster Pressure Sensor Circ…P0558Brake Booster Pressure Sensor Circ…P0559Brake Booster Pressure Sensor Circ…P2616Camshaft Position Signal Intermitt…

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