ABS Inspection Bulletin - ABS Malfunction Lamp Operation

The following, noted bulletin contains language that lends itself to conflicting interpretations. Bulletin: ABS Inspection Procedure U.S Field Reference Air Brake Equipped Vehicles (Revision Date: January, 2015); and Antilock Brake System (ABS) Inspections (Revision Date: September 19, 2013) Bulletin Number: 2013-02

The ABS malfunction lamp is a MIL (Malfunction Indicator Lamp) and must be functional. This light must: 1. BE PRESENT. a. Based on date of manufacture vehicle are required to be equipped with antilock brake systems ABS. i. Manufacture dates dictate requirement timelines for trucks truck/tractors and trailers. Additionally, the timeline for communication between the towing and towed vehicle is defined. b. The vehicles of interest for this request are those that are required to have ABS. 2. CAPABLE OF SIGNALING A MALFUNCTION. a. The light must be operational (must illuminate) when power is supplied to the ABS ECU. b. SIGNAL MUST BE PRESENT WHENEVER THERE IS A MALFUNCTION THAT AFFECTS THE GENERATION OR TRANSMISSION OF RESPONSE OR CONTROL SIGNALS IN THE ANTILOCK BRAKE SYSTEM. i. The signal must remain present anytime there is power supplied to the antilock brake system. 3. THE ANTILOCK BRAKE SYSTEM MUST BE ABLE TO STORE MALFUNCTION MESSAGES WHEN THE POWER IS REMOVED. 4. MALFUNCTION MESSAGES MUST REACTIVATE WHEN POWER IS REAPPLIED. Under a current interpretation of these bulletins violations are being assigned when upon supplying power to the ABS ECU the MIL lights (either/or Truck Tractor or Trailer) the light cycles and then comes back on. When this happens the ABS Malfunction Indicator Lamp has validated that it is functioning proper and should not be a violation. 1. Upon application of power the light turns on the MIL (IT IS PRESENT). 2. It will stay on for approximately 3 seconds during the self-test. 3. The MIL light goes out indicating completion of the self. a. The light remains out, no system faults are present. b. The light comes back on. (IT IS DEMONSTRATING MALFUNCTION SIGNALING ) i. There is either an active DTC or; ii.There is a stored DTC that has not been cleared. The light is doing what it is supposed to do. It is warning the driver of a system malfunction that needs to be reported and repaired. A driver having been notified via the Malfunction Indicator Lamp can perform a test to further assess the system status. The light is not necessarily an indicator that the vehicles ABS is not functional. An excerpt from a Bendix Service DATA publication states, “The ECU will illuminate the ABS Indicator Lamp whenever full ABS operation is not available due to a diagnostic trouble code. In most cases, partial ABS is still available.”

ABS Inspection Procedure U.S Field Reference Air Brake Equipped Vehicles (Revision Date: January, 2015) At the end of the first sentence it reads “… powering the ABS system off and on and confirming whether the ABS malfunction shows violations”. “Violations” should be removed as the light is identifying a malfunction or fault but not necessarily a violation. Antilock Brake System (ABS) Inspections (Revision Date: September 19, 2013) - Bulletin Number: 2013-02 1.Page 3 – ABS Functional Status The last sentence reads, “A problem (and a violation) is present either when the ABS malfunction lamp fails to turn on when power is applied to the ABS or when the lamp turns on and stays on”. The first half of the sentence is good it is the last half that is not clear. A distinction needs to be made between a MIL that: • Comes on, goes out after approximately 3 second and then comes back on (which should not be a violation) and; • A MIL that comes on and as the document states stays on (which would be a violation). 2. Page 5 – Step by Step Inspection Procedure – Item #2 This needs to be clarified the difference between a MIL that illuminates and stays lit without cycling (a violation) and one that illuminates, completes the self-diagnostics and then illuminates (not a violation).1 3. Page 6 – Table Rows 2 and 3 need to clarify that the light did not cycle – it came on and stayed on without interruption. 4. Page 6 – Item 6(b) Clarification that I this is the case if the light comes and stays on without the cycling that indicated the completion of the diagnostic step. 1 On some vehicles the trailer auxiliary wire may be shared for a secondary reason. In this case it may be necessary to interrupt the power to the ABS ECU. This is addressed in in the last step of the ABS Inspection.