Symptom Chart — Rear Brake Anti-Lock Control

There are times when a customer concern will not cause the yellow REAR ABS warning light to illuminate or a code to be stored.

The symptom chart is intended to give the technician a starting point in resolving these types of concerns. The chart also describes conditions that will illuminate the yellow RABS light.

Please note that both the red BRAKE warning light diagnosis procedure and test drive are required prior to performing the tests in this section. Failure to perform these procedures will greatly diminish the effectiveness of this method of diagnosis.

SYMPTOM CHART — REAR BRAKE ANTI-LOCK CONTROL

Condition	Possible Source	Action
Red Brake Warning Light Does Not Self-Check	Open brake warning light bulb (red). Open power fuse. Open Circuit 640 (R/Y), 977 (P/W), 512 (T/LG), 531 (DG/Y). Open resistor/diode circuit. Unseated fluid level switch connector. Defective ignition switch.	GO to Pinpoint Test A.
Red Brake Warning Light Stays On When Key Is in RUN Position	Ground short on Circuit 977. Ground short on Circuit 162. Damaged parking brake switch. Damaged low vacuum switch.	GO to Pinpoint Test B.
Yellow Rear ABS Warning Light Off and Does Not Self-Check	Open fuse Circuit 640 (R/Y). Missing power to rear ABS warning light (open Circuit 640 [R/Y]). Open Circuit 603 (DG). Burned-out yellow REAR ABS warning light. Terminal backout in the anti-lock electronic control module harness connector at Pin 7. Harness connector not fully mated with anti-lock electronic control module. Defective anti-lock electronic control module. Open anti-lock electronic control module ground (Circuit 570 [BK/W] or Circuit 530 [LG/Y]).	GO to Pinpoint Test C.
Yellow Rear ABS Warning Light Self-Check OK, but Light Automatically Begins Flashing	Intermittent anti-lock electronic control module. Intermittent anti-lock electronic control module ground circuit. Intermittent yellow rear ABS warning light circuit. Blown Keep-Alive Memory fuse.	GO to Pinpoint Test D.
Yellow Rear ABS Warning Light Self-Check OK, but No Diagnostic Trouble Code When Diagnostics Are Started	Burned-out brake taillights. Missing anti-lock electronic control module power (Circuit 601 [LB/PK] and associated fuse). Shorted yellow rear ABS warning light circuit (Circuit 603 [DG]). Incorrect anti-lock electronic control module (RABS I vs. RABS II).	GO to Pinpoint Test E.
Yellow Rear ABS Warning Light Flashes Two Times When Retrieving Diagnostic Trouble Codes (Code 2)	Terminal backout in the anti-lock electronic control module harness connector at Pin 13. Terminal backout in the RABS valve harness connector at Pin 1. Bulkhead connector (between engine compartment and instrument panel) terminal backout or loose connection. Anti-lock electronic control module or RABS valve connectors not fully mated with component. Intermittent open circuit in Circuit 599 (PK/LG).	GO to Pinpoint Test F.
Yellow Rear ABS Warning Light Flashes Three Times When Retrieving Diagnostic Trouble Codes (Code 3)	Terminal backout in the anti-lock electronic control module harness connector at Pin 8 or 14. Terminal backout in the RABS valve harness connector at Pin 4. Bulkhead connector (between engine compartment and instrument panel) terminal backout or loose connection. Anti-lock electronic control module or RABS valve connectors not fully mated with component. Intermittent open circuit in Circuit 664 (Y/LG).	GO to Pinpoint Test G.
Yellow Rear ABS Warning Light Flashes Four Times When Retrieving Diagnostic Trouble Codes (Code 4)	Terminal backout in the anti-lock electronic control module harness connector at Pin 6. Terminal backout in the RABS valve harness connector at Pins 2 or 3. Bulkhead connector (between engine compartment and instrument panel) terminal backout or loose connection. Anti-lock electronic control module or RABS valve connectors not fully mated with component. Intermittent open or open circuit in Circuits 535 (LB/R) or 274 (BK/W). Intermittent short or short circuit in Circuit 535 (LB/R). Defective RABS valve.	GO to Pinpoint Test H.
Yellow Rear ABS Warning Light Flashes Five Times When Retrieving Diagnostic Trouble Codes (Code 5)	Parking brake drag. Worn or damaged 4x4 switch (4x4 only). Rear brake assembly grabby or hanging up. Connector corrosion or contamination. Intermittent open circuit in Circuit 210 (LB). Pierced wire insulation to battery power (4x4 only).	GO to Pinpoint Test J.
Yellow Rear ABS Warning Light Flashes Six Times When Retrieving Diagnostic Trouble Codes (Code 6)	Terminal backout in the anti-lock electronic control module harness connector at Pins 3 and 10. Terminal backout in the RABS sensor harness connector at Pins A and B. Bulkhead connector (between engine compartment and instrument panel) terminal backout or loose connection. Anti-lock electronic control module or RABS sensor connectors not fully mated with component. Intermittent open/short circuit in Circuits 519 (LG/BK) or 523 (R/PK). Damaged RABS sensor (possibly metal shavings on pole piece). Damaged RABS sensor ring (possibly teeth missing).	GO to Pinpoint Test K.
Yellow Rear ABS Warning Light Flashes Seven Times When Retrieving Diagnostic Trouble Codes (Code 7)	Anti-lock electronic control module fuse blown or internal open circuit. Shorted isolation solenoid internal to the RABS valve. Intermittent short or shorted circuit in Circuit 599 (PK/LG). Contamination or bent Pins 1 and 3 of RABS valve connector shorting together.	GO to Pinpoint Test L.
Yellow Rear ABS Warning Light Flashes Eight Times When Retrieving Diagnostic Trouble Codes (Code 8)	Anti-lock electronic control module internal fuse blown or internal open circuit. Shorted dump solenoid internal to the RABS valve. Intermittent short or shorted circuit in Circuit 664 (Y/LG). Bulkhead connector between engine compartment and instrument panel terminals shorted.	GO to Pinpoint Test M.
Yellow Rear ABS Warning Light Flashes Nine Times When Retrieving Diagnostic Trouble Codes (Code 9)	Terminal backout in the anti-lock electronic control module harness connector at Pin 3 or Pin 10. Terminal backout in the RABS sensor harness connector at Pins A or B. Anti-lock electronic control module or RABS sensor connectors not fully mated with component. Open or intermittent open circuits in Circuit 519 (LG/BK) or 523 (R/PK).	GO to Pinpoint Test N.
Yellow Rear ABS Warning Light Flashes 10 Times When Retrieving Diagnostic Trouble Codes (Code 10)	Short between anti-lock electronic control module harness connector Pin 3 and Pin 10. Short between RABS sensor connector Pins A and B. Bulkhead connector (between engine compartment and instrument panel) terminals shorted together. Intermittent short circuit in Circuits 519 (LG/BK) or 523 (R/PK).	GO to Pinpoint Test P.
Yellow Rear ABS Warning Light Flashes 11 Times When Retrieving Diagnostic Trouble Codes (Code 11)	Terminal backout in the anti-lock electronic control module harness connector at Pin 11. Missing (burned-out) stoplamps. All stoplamps must be missing or burned out to cause a Code 11. An intermittent/continuous open in Circuit 511 (LG). This open would be between anti-lock electronic control module connector Pin 11 and the stoplight switch. Worn or damaged stoplight switch.	GO to Pinpoint Test Q.
Yellow Rear ABS Warning Light Flashes 12 Times When Retrieving Diagnostic Trouble Codes (Code 12)	Low level in brake master cylinder reservoir. Fluid leaks in vehicle brake system. Worn or damaged fluid level switch, or fluid level switch circuit shorted to ground. Brake master cylinder reservoir float that sticks in the bottom of brake master cylinder reservoir or does not float. Failed diode/resistor element in stoplamp circuit. Damaged ignition switch. Ground short in Circuits 512 (T/LG) or 531 (DG/Y). Damaged anti-lock electronic control module.	GO to Pinpoint Test R.
Yellow Rear ABS Warning Light Flashes 13 Times When Retrieving Diagnostic Trouble Codes (Code 13)	Anti-lock electronic control module is damaged.	REPLACE anti-lock electronic control module. GO to Pinpoint Test S. TEST drive vehicle.
Yellow Rear ABS Warning Light Flashes 16 Times When Retrieving Diagnostic Trouble Codes (Code 16)	No codes stored in anti-lock electronic control module.	STOP. Rear anti-lock brake system functioning properly.
Intermittent Problem Suspected	Intermittent voltage to anti-lock electronic control module. Less than 11 volts to anti-lock electronic control module. Intermittent connections at speed sensor, RABS valve, anti-lock electronic control module.	GO to Pinpoint Test T.
Rear ABS and Speedometer Are Not Functioning Correctly	No signal from RABS sensor. Defective RABS sensor.	GO to Pinpoint Test U.
Unwarranted RABS Activity	Metal chips on RABS sensor pole piece.	REFER to Pinpoint Test K, step K6 only.
	Gap between RABS sensor and RABS sensor ring is too large (greater than 1.14mm [0.045 inch]).	REFER to Pinpoint Test K, steps K11 and K12 only.
	Missing or damaged RABS sensor ring teeth.	REFER to Pinpoint Test K, step K13 only.
	RABS sensor/sensor ring interference — gap is too small (less than 0.127mm [ 0.005 inch]).	REFER to Pinpoint Test K, step K13 only.
	Intermittent open or shorted RABS sensor circuit.	PERFORM intermittent diagnosis for Circuits 519 (LG/BK) and anti-lock electronic control module and RABS sensor.
	Intermittent open RABS sensor circuit at intermediate connections, especially bulkhead.	PERFORM intermittent diagnosis for Circuit 519 (LG/BK) and 523 (R/PK) at intermediate connectors.
	Chafed wire insulation or pinched wire.	INSPECT wiring harness from rear axle assembly to frame side rail for chafing or rub marks.
	Rear brake adjustment too tight.	REFER to Section 06-00.
	Linings are "grabby."	REFER to Section 06-00.
One or Both Rear Wheels Lock Up	Damaged RABS valve reset switch.	REFER to Pinpoint Test H, steps H11 and H14 only.
	Leaky isolation valve.	REFER to Pinpoint Test H, step H13 only.
	RABS sensor air gap too large.	REFER to Pinpoint Test K, step K11 only.
	RABS sensor/sensor ring assembly does not produce sufficient output.	REFER to Pinpoint Test K, step K10 only. PERFORM intermittent diagnosis for Circuit 519 (LG/BK) and 523 (R/PK) between anti-lock electronic control module and RABS sensor. PERFORM intermittent diagnosis for Circuit 519 (LG/BK) and 523 (R/PK) at intermediate connectors.
	Brake related concern: Damp or contaminated rear brake shoe linings.Stuck/leaking rear wheel cylinder.Rear brake adjusted too tight.	REFER to Section 06-00.
	Hung-up parking brake.	REFER to Section 06-00.
	Hubs engaged although shift lever is in 4x2 position.	REFER to Section 07-07.
	Faulty 4x4 indicator switch or short to 12v in 4x4 Circuit 210 (LB).	REFER to Pinpoint Test J, steps J3 and J5 only.
	Stoplamp input to anti-lock electronic control module not present.	REFER to Pinpoint Test Q, steps Q1-Q4 only.
	Stoplamps inoperative.	REFER to Section 17-01.
Hard or Soft Brake Pedal	Stuck shut isolation valve (hard).	REFER to Pinpoint Test H, step H14 only.
	Leaky dump valve (soft).	REFER to Pinpoint Test H, step H13 only.
	Leaky isolation valve during RABS stop (soft).	REFER to Pinpoint Test J, step J9 only.
	Stoplamps always on while driving.	REFER to Pinpoint Test Q, steps Q1-Q4 only.
	Hydraulic leak in rear brake tube or rear brake hose, fitting, brake master cylinder, rear wheel cylinder, or front disc brake caliper.	REFER to Section 06-00.
	Air in brake system.	REFER to Section 06-00.
	Brake related concern:Little or no vacuum boost.Stuck or inoperative rear wheel cylinder or front disc brake caliper.Pinched or crimped rear brake tube or rear brake hose.	REFER to Section 06-00.
Lack of Deceleration During Medium/Hard Brake Applications	Leaky dump valve.	REFER to Pinpoint Test H, step H13.
	Stuck shut isolation valve.	REFER to Pinpoint Test H, step H14 only.
	Short/open in frame or instrument panel harness (Circuits 519 [LG/BK] and/or Circuit 523 [R/PK]).At anti-lock electronic control module connector (Pins 3 and 10).At RABS sensor connector.At bulkhead or other interconnection.Pinched wire or worn insulation due to improper routing.RABS sensor test connector (in engine compartment).	REFER to Pinpoint Test K, steps K1-K5 only.
	Metal chips on RABS sensor.	REFER to Pinpoint Test K, step K6 only.
	Borderline high RABS sensor to RABS sensor ring air gap, excessive RABS sensor ring radial runout, damaged or missing RABS sensor ring teeth.	REFER to Pinpoint Test K, steps K11 and K12 only.
	Low vacuum switch inoperative (diesel only).	REFER to Section 06-00.
	Hydraulic leak in brake line tubing or rear brake hose, fitting, brake master cylinder, rear wheel cylinder, or front disc brake caliper.	REFER to Section 06-00.
	Air in brake system.	REFER to Section 06-00.
	Brake related concern:Little or no vacuum boost.Stuck or inoperative wheel cylinder or caliper.Pinched or crimped rear brake hose or brake line tubing.Ineffective brake shoe or pad linings.	REFER to Section 06-00.