Symptom Chart — 4-Wheel Anti-Lock Brakes

The symptom chart is intended to give the technician a starting point in resolving these types of problems. Again, the system precheck must be performed prior to consulting the symptom chart to verify other diagnostic trouble codes have not been set, and to maximize the effectiveness of this method of diagnosis.

NOTE: Perform indicated pinpoint test or specified test steps only — do not perform other steps (although within the test box, you may appear to be directed to do so). Always return to the symptom chart if no resolution is reached by performing a particular test.

SYMPTOM CHART — 4-WHEEL ANTI-LOCK BRAKES

Condition	Possible Source	Action
Code 11 Retrieved	Anti-lock brake electronic control module failure.	REPLACE anti-lock brake electronic control module.
Code 16 Retrieved	System OK.	None.
Reference Voltage/Intermittent Valve Fault (Code 17)	30 amp fuse open. Intermittent connections to battery, main relay or ground. Main relay coil or contacts open. Open or short to ground in Circuit 532 (O/Y). Open or short to ground in Circuit 599 (PK/LG). Open or short to ground in Circuit 601 (LG/PK). Short to ground through anti-lock hydraulic control unit. Intermittent valve failures. High resistance valves.	GO to Pinpoint Test A.
Front Left Inlet Solenoid Valve Concern Diagnosis (Code 22)	Intermittent open Circuit 495 (T). Terminal backout in anti-lock brake electronic control module connector Pins 17 and 40. Terminal backout in anti-lock hydraulic control unit connector Pins 1, 4 and 6. Open or shorted inlet front left valve coil. Open or shorted driver in anti-lock brake electronic control module.	GO to Pinpoint Test B.
Front Left Outlet Solenoid Concern Diagnosis (Code 23)	Intermittent open Circuit 496 (O). Terminal backout in anti-lock brake electronic control module connector Pins 17 and 26. Terminal backout in anti-lock hydraulic control unit connector Pins 1, 4 and 7. Open or shorted outlet front left valve coil. Open or shorted driver in anti-lock brake electronic control module.	GO to Pinpoint Test C.
Front Right Inlet Solenoid Valve Concern Diagnosis (Code 24)	Intermittent open Circuit 497 (W). Terminal backout in anti-lock brake electronic control module connector Pins 17 and 34. Terminal backout in anti-lock hydraulic control unit connector Pins 1, 4 and 8. Open or shorted inlet front right valve coil. Open or shorted driver in anti-lock brake electronic control module.	GO to Pinpoint Test D.
Front Right Outlet Solenoid Valve Concern Diagnosis (Code 25)	Intermittent open Circuit 498 (PK). Terminal backout in anti-lock brake electronic control module connector Pins 17 and 15. Terminal backout in anti-lock hydraulic control unit connector Pins 1, 4 and 5. Open or shorted outlet front right valve coil. Open or shorted driver in anti-lock brake electronic control module.	GO to Pinpoint Test E.
Rear Axle Inlet Solenoid Valve Concern Diagnosis (Code 26)	Intermittent open Circuit 499 (GY/BK). Terminal backout in anti-lock brake electronic control module connector Pins 17 and 33. Terminal backout in anti-lock hydraulic control unit connector Pins 1, 4 and 2. Open or shorted inlet rear axle valve coil. Open or shorted driver in anti-lock brake electronic control module.	GO to Pinpoint Test F.
Rear Axle Outlet Solenoid Concern Diagnosis (Code 27)	Intermittent open Circuit 510 (T/R). Terminal backout in anti-lock brake electronic control module connector Pins 17 and 27. Terminal backout in anti-lock hydraulic control unit connector Pins 1, 4 and 3. Open or shorted outlet rear axle valve coil. Open or shorted driver in anti-lock brake electronic control module.	GO to Pinpoint Test G.
Left Front Brake Anti-Lock Sensor Diagnosis (Static) (Code 31)	Poor connection at left front brake anti-lock sensor. Terminal damage or backout in anti-lock brake electronic control module connector Pins 24 and 25. Terminal damage or backout in two-pin sensor connector. Open or shorted left front brake anti-lock sensor. Open or shorted Circuit 521 (T/O) or 522 (T/BK). Improper front left anti-lock brake sensor cable routing leading to above. Defective front left wheel speed sensor electrical test circuit in anti-lock brake electronic control module.	GO to Pinpoint Test H.
Right Front Brake Anti-Lock Sensor Diagnosis (Code 32)	Poor connection at right front brake anti-lock sensor. Terminal damage or backout in anti-lock brake electronic control module connector Pins 36 or 23. Terminal damage or backout in two-pin anti-lock brake sensor connector. Open or shorted right front brake anti-lock sensor. Open or shorted Circuit 514 (Y/R) or 516 (Y/BK).	GO to Pinpoint Test J.
Rear Axle Speed Sensor Diagnosis (Code 33)	Poor connection at vehicle speed sensor. Terminal damage or backout in anti-lock brake electronic control module connector Pins 21 or 22. Terminal damage or backout in two-pin sensor connector. Open or shorted vehicle speed sensor coil. Open or shorted Circuit 518 (LG/R) or 519 (LG/BK). Improper vehicle speed sensor cable routing leading to above. Defective vehicle speed sensor electrical test circuit in anti-lock brake electronic control module. NOTE: Some vehicles were built using Circuit 523 (R/PK) in place of 518 (LG/R).	GO to Pinpoint Test K.
Left Front Brake Anti-Lock Sensor Diagnosis (Dynamic) (Codes 35, 41, 55, 75)	Damaged/missing front brake anti-lock sensor indicator teeth or missing front brake anti-lock sensor indicator. Air gap too small or too large. Excessive axle vibration. Weak front brake anti-lock sensor. Loose front brake anti-lock sensor. INTERMITTENT short or open in Circuit 521 (T/O) or 522 (T/BK). Disturbances caused by ignition or radio frequency interference. Defective trigger circuit in anti-lock brake electronic control module.	GO to Pinpoint Test L.
Right Front Brake Anti-Lock Sensor Diagnosis (Dynamic) (Codes 36, 42, 56, 76)	Damaged/missing front brake anti-lock sensor indicator teeth or missing front brake anti-lock sensor indicator. Air gap too small or too large. Excessive axle vibration. Weak front brake anti-lock sensor. Loose front brake anti-lock sensor. INTERMITTENT short or open in Circuit 514 (Y/R) or 516 (Y/BK). Disturbances caused by ignition or radio frequency interference. Defective trigger circuit in anti-lock brake electronic control module.	GO to Pinpoint Test M.
Rear Axle Speed Sensor Diagnosis (Dynamic) (Codes 37, 43, 57, 77)	Damaged/missing indicator ring teeth or missing indicator ring. Air gap too small or too large. Excessive axle vibration. Weak rear axle sensor. Loose rear axle sensor. Intermittent short or open in Circuit 518 (LG/R) or 519 (LG/BK). NOTE: Some vehicles were built using Circuit 523 (R/PK) in place of 518 (LG/R). Disturbances caused by ignition or radio frequency interference. Defective trigger circuit in anti-lock brake electronic control module.	GO to Pinpoint Test N.
Hydraulically Inoperative Front Left Outlet Valve or Sensor Disturbance Detected Diagnosis (Code 51)	Pinched or closed brake line or hose. Worn or clogged front left outlet valve.	GO to Pinpoint Test P.
Hydraulically Inoperative Right Front Outlet Valve or Sensor Disturbance Detected Diagnosis (Code 52)	Pinched or closed brake line or hose. Worn or clogged front right outlet valve.	GO to Pinpoint Test Q.
Hydraulically Inoperative Rear Axle Outlet Valve or Sensor Disturbance Detected Diagnosis (Code 53)	Pinched or closed brake line or hose. Worn or clogged rear axle outlet valve.	GO to Pinpoint Test R.
Pump Motor Triggered but Did Not Run (Code 63)	Damaged pump motor. Terminal backout in anti-lock brake electronic control module harness connector Pins 17, 29, 37 and 38. Open or shorted pump motor relay coil. Open contacts in pump motor relay. Terminal backout in pump motor 4-way, Pins 1, 2, 3 or 4.	GO to Pinpoint Test S.
Acceleration Sensor (Code 65)	Terminal backout in anti-lock brake electronic control module wiring harness connector Pins 30, 31 and 32. Worn or damaged acceleration switch. Worn or damaged anti-lock brake electronic control module. Acceleration switch terminal backout, Pins 1, 2 and 3. Short to ground in Circuits 836 (O/W), 886 (O/BK) and 887 (Y).	GO to Pinpoint Test T.
Pump Motor Running but Not Triggered (Code 67)	Damaged trigger circuit in anti-lock brake electronic control module. Terminal backout in anti-lock brake electronic control module harness connector Pins 2 and 3. Welded relay contacts. Short to ground in Circuit 539 (PK/LB).	GO to Pinpoint Test U.
Amber ABS Warning Lamp On, No Code	Worn or damaged ignition switch. Open ignition feed circuit to anti-lock brake electronic control module. Low battery voltage (less than 8V). Blown ignition fuse. Open system ground.	GO to Pinpoint Test V.
Intermittent Diagnosis	Intermittent problem.	GO to Pinpoint Test W.
Diagnostic Trouble Code or Concern Symptom Not Known	Any of the above possible sources.	GO to Pinpoint Test X.
ABS and Speedometer Are Not Functioning Properly	No signal to anti-lock brake electronic control module from vehicle speed sensor. Defective vehicle speed sensor.	GO to Pinpoint Test Y.
Unwarranted ABS Activity	Tone ring is damaged.	INSPECT both front brake anti-lock sensor indicators and the rear axle tone ring.
	Sensor output is weak.	Left front brake anti-lock sensor — GO to Pinpoint Test L. Right front brake anti-lock sensor — GO to Pinpoint Test M. Rear axle sensor — GO to Pinpoint Test N.
	Intermittent open or shorted sensor circuit. Intermittent open sensor circuit at intermediate connections especially bulkhead.	GO to Pinpoint Test W.
	Chafed wire insulation or pinched wire due to improper routing causing intermittent short.	INSPECT wiring harness from front brake anti-lock sensors on knuckle to the frame and from the rear axle to the frame for worn or chafed wire insulation.
	Rear brake adjustment too tight. Linings are "grabby".	REFER to Section 06-00.
Wheels Lock Up	Hydraulic outlet (dump) valve.	Left front wheel — REFER to Pinpoint Test P, Steps P2 and P3 ONLY. Right front wheel — REFER to Pinpoint Test Q, Steps Q2 and Q3 ONLY. Rear axle — REFER to Pinpoint Test R, Steps R2 and R3 ONLY.
	Damp or contaminated rear brake shoe linings, stuck/leaking wheel cylinder, overadjusted rear brakes. Hung-up parking brake.	REFER to Section 06-00.
	Leaking rear axle seal.	REFER to the appropriate section in Group 05.
Hard or Soft Brake Pedal	Stuck shut inlet (isolation) valve (hard) or leaky outlet (dump) valve (soft).	Left front wheel — REFER to Pinpoint Test P, Steps P2 and P3 ONLY. Right front wheel — REFER to Pinpoint Test Q, Steps Q2 and Q3 ONLY. Rear axle — REFER to Pinpoint Test R, Steps R2 and R3 ONLY.
	Leaky inlet (isolation) valve during ABS (soft).	Left front wheel — REFER to Pinpoint Test P, Steps P2 and P3 ONLY. Right front wheel — REFER to Pinpoint Test Q, Steps Q2 and Q3 ONLY. Rear axle — REFER to Pinpoint Test R, Steps R2 and R3 ONLY.
	Hydraulic leak in brake line or hose, fitting, brake master cylinder, wheel cylinder, or caliper. Air in brake system. Little or no vacuum boost. Stuck or inoperative wheel cylinder or caliper. Pinched or crimped brake line or hose.	REFER to Section 06-00.
Lack of Deceleration During Medium/Hard Brake Application	Stuck shut inlet (isolation) valve or leaky outlet (dump) valve — rear axle ONLY.	Rear axle — REFER to Pinpoint Test R, Steps R2 and R3 ONLY.
	Hydraulic leak in brake line or hose, fitting, brake master cylinder, wheel cylinder, or caliper. Air in brake system. Little or no vacuum boost. Stuck or inoperative wheel cylinder or caliper. Pinched or crimped brake line or hose. Ineffective brake shoe or pad linings.	REFER to Section 06-00.
Vehicle Pulls During Braking	Fully or partially blocked right front inlet (isolation) valve.	Right front wheel — REFER to Pinpoint Test Q, Steps Q2 and Q3 ONLY.
	Fully or partially blocked left front inlet (isolation) valve.	Left front wheel — REFER to Pinpoint Test P, Steps P2 and P3 ONLY.
	Improperly adjusted rear brake. Frozen or binding caliper (one side of vehicle). Uneven brake pad or shoe wear. Pinched or crimped brake line or hose.	REFER to Section 06-00.
ABS Warning Light On Intermittently with Code 16	Ignition circuit 601 loose.	INSPECT Circuit 601 harness from ignition switch to anti-lock brake electronic control module harness connector for opens/shorts especially at the bulk-head connector. CORRECT as necessary.
	Loose anti-lock brake electronic control module grounds.	INSPECT anti-lock brake electronic control module grounds for looseness, corrosion or excessive dirt. CORRECT as necessary.
	Loose power log at power distribution box.	CORRECT and REPAIR as necessary.
	Low battery/charging system.	VERIFY ABS warning light does not come on at idle with high electrical loads.