Mechanics

2500 ANTI-LOCK BRAKE LIGHT

1998 Mazda b2500 • 4 cylinder 2WD Manual • 127 miles

I have a 1998 Mazda B2500 XLT 2WD. The anti-lock brake light stays on. I have replaced the rear speed sensor, but it didn't fix the problem. Are there other common sources for this condition?
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Tjglakas
February 5, 2011.



There are many ABS codes, and to avoid throwing parts at it, have it scanned by any shop that can read "C" and "U" codes. A scan will pinpoint the bad part(s).


Merlin2021
Feb 5, 2011.
Thanks - I'm not one to troubleshoot by replacing parts, but this was a quick and easy (and inexpensive) swap out. I took it to one shop to read the code and they said nothing came up. My understanding is that there is only one speed sensor. Is this correct?


Tiny
Tjglakas
Feb 5, 2011.
There are two systems for this truck, two wheel and four wheel ABS it sounds like you have a power supply to the ABS unit problem, when the power is interupted, the yellow abs light comes on, but no codes are stored, chech fuses for abs and wiring harness that powers the abs mod, here are the part locations.
By the book: RABS Self-Test Capability
RABS module performs a system test during start-up and normal operation. Red BRAKE warning
light indicates low fluid level or parking brake applied. If a problem is detected, the module will be
deactivated and a Yellow ABS warning light will be illuminated. Both warning lights should
illuminate for about 2 seconds when ignition is turned on or when cranking engine.
When Yellow ABS warning light illuminates during normal operation, the system has detected a
problem and stored a Diagnostic Trouble Code (DTC). Loss of power to module will cause system to
be deactivated and Yellow ABS warning light to be illuminated, but will not set a DTC.


Merlin2021
Feb 5, 2011.
You could also just be low on brake fluid!


Merlin2021
Feb 5, 2011.
Thanks - let me look into that.


Tiny
Tjglakas
Feb 5, 2011.
Good on brake fluid, fuses, diode, and resistor good. Reseated connectors on all components. Everything works as advertised (abs/brake lights on 2 sec then off) when starting. ABS light comes on at 12-15 MPH. Your table above says the ABS diagnostic connector is behind the RH dash, though I don't see it. Maybe the shop tried to pull the code from teh engine diagnostic plug in error.


Tiny
Tjglakas
Feb 5, 2011.
Are you sure yours is two wheel ABS?
Test this way: YELLOW ABS WARNING LIGHT SELF-CHECKS OKAY, BUT AUTOMATICALLY
BEGINS FLASHING

1. Observe ABS Warning Light For Flash Sequence - Turn ignition on. Observe Yellow ABS
warning light. If Yellow ABS warning light flashes a DTC sequence, note DTC and go to next
step. If Yellow ABS warning light flashes, but does not indicate a DTC, go to step 4).
2. Check Voltage To RABS Module - Turn ignition off. Disconnect 14-pin RABS module
connector. Turn ignition on. Using DVOM, check voltage between RABS module connector
terminal No. 12 (Black/Orange wire) and ground while wiggling wiring harness. See WIRING
DIAGRAMS. If voltage is greater than 10 volts, go to next step. If voltage is not greater than
10 volts, repair Black/Orange wire or Red wire between RABS module and fuse panel.
Perform appropriate test for DTC retrieved.
3. Check RABS Module Ground - Turn ignition off. Using DVOM, check resistance between
RABS module connector terminal No. 4 (Light Green/Yellow wire) and ground while wiggling
wiring harness. See WIRING DIAGRAMS. If resistance is less than 5 ohms, replace RABS
module. Recheck system operation. If resistance is not less than 5 ohms, repair Light
Green/Yellow wire and/or Black/Light Blue wire between RABS module and ground
connection. Recheck system operation.
4. Check Voltage To RABS Module - Turn ignition off. Disconnect 14-pin RABS module
connector. Turn ignition on. Using DVOM, check voltage between RABS module connector
terminal No. 1 (Light Blue/Pink wire) and ground. See WIRING DIAGRAMS. Using
DVOM, check voltage between RABS module connector terminal No. 9 (Light Blue/Pink
wire) and ground. If voltage is greater than 10 volts, replace RABS module. Recheck system
operation. If voltage is not greater than 10 volts, repair Light Blue/Pink wire between RABS
module and fuse panel.
YELLOW ABS WARNING LIGHT SELF-CHECKS, BUT NO DTCS ARE RETRIEVED
WHEN DIAGNOSTICS ARE STARTED

1. Check Brown Wire Circuit For Open - Disconnect Brake Pedal Position (BPP) switch
connector. Turn ignition on. Using DVOM, check voltage between BPP switch connector
terminal No. 3 (Brown wire) and ground. See WIRING DIAGRAMS. If voltage is greater
than 10 volts, go to next step. If voltage is not greater than 10 volts, repair Brown wire between
BPP switch and instrument panel fuse panel. Recheck system operation.
2. Check Brake Pedal Position (BPP) Switch Input To RABS Module - Turn ignition off.
Disconnect 14-pin RABS module connector. Depress brake pedal. Using DVOM, check
voltage between RABS module connector terminal No. 11 (Red/Light Green wire) and ground.
See WIRING DIAGRAMS. If voltage is greater than 10 volts, go to next step. If voltage is
not greater than 10 volts, repair Red/Light Green wire between RABS module and BPP switch.
Recheck system operation.
3. Check Voltage To RABS Module - Turn ignition on. Using DVOM, check voltage between
RABS module connector terminal No. 1 (Light Blue/Pink wire) and ground. See WIRING
DIAGRAMS. Using DVOM, check voltage between RABS module connector terminal No. 9
(Light Blue/Pink wire) and ground. If voltage is greater than 10 volts, go to next step. If
NOTE: DTC will appear as one or more short pulses followed by one long
pulse.
Voltage is not greater than 10 volts, repair Light Blue/Pink wire between RABS module and
instrument panel fuse panel. Recheck system operation.
4. Check Keep Alive Memory (KAM) Power Circuit - Turn ignition off. Disconnect RABS
diagnostic connector. Using DVOM, check resistance between RABS module connector
terminal No. 12 (Black/Orange wire) and RABS diagnostic connector Black/Orange wire
terminal. See WIRING DIAGRAMS. If resistance is less than 5 ohms, replace RABS
module. Recheck system operation. If resistance is not less than 5 ohms, repair Black/Orange
wire between RABS module and RABS diagnostic connector. Recheck system operation.


Merlin2021
Feb 7, 2011.
Thanks Merlin will run through this and see what I come up with. I'm sure it's RABS and not 4-wheel. Seems like it's not getting speed input from either the speedo or rear speed sensor, as the light goes off on engine start, but comes on consistently at 12 MPH. Where can I get wiring diagrams for the RABS?


Tiny
Tjglakas
Feb 12, 2011.
Rightr here


Merlin2021
Feb 13, 2011.
This is great! Thanks very much!


Tiny
Tjglakas
Feb 13, 2011.
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