OK here is what I'm working on. Im at R5. when the parking brake in on am i looking for a ground in the DG / Y wire? meaning if there is a ground there is a problem??? and where is the resistor/diode element?

what i have is ABS light is on. I dont get a red brake light when the float in the reservoir is pushed down or when I hot wire the plug, the signal is not making it to the light and or????? I do have a good ground at the Reservoir plug.



Description: Code 12 is generated when the anti-lock electronic control module detects that the brake fluid level in the brake master cylinder reservoir is low for one or more seconds during an anti-lock stop. It can also be generated by a short in the stoplamp circuit.

Possible Contributing Base Brake Component/Vehicle Wiring Concerns

Low master cylinder fill level

Fluid leaks in vehicle brake system

Worn or damaged master cylinder , or fluid level circuit shorted to ground

Master cylinder 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 or 531

Damaged anti-lock electronic control module

R1: CHECK WARNING LIGHTS

Key OFF.

Locate and disconnect the diagnostic connector from its mating half (Circuits 571 [BK/O] and 483 [R]).

Reconnect diagnostic connector.

Key ON.

Do BOTH the red BRAKE and yellow RABS lamps come on?

Yes: Hard fault. GO to «R2».

No: If the brakes have been serviced recently, or if brake fluid has been added to the system recently, MOST likely, the Code 12 was falsely set at that time and the RABS is OK. If this is NOT the case, GO to «Test T» for intermittent diagnosis procedures for the affected circuits. REFER to the mini-schematic for this pinpoint test.

R2: CHECK BRAKE FLUID LEVEL IN MASTER CYLINDER

Key OFF.

Check the brake fluid level in the brake master cylinder reservoir.

Is the fluid level within specification?

Yes: GO to «R3».

No: CHECK for leaks in the brake system. REPAIR as required. FILL brake master cylinder reservoir to the required level. GO to «R9».

R3: VERIFY FLOAT BUOYANCY

Remove the .

Attempt to push down the float with a clean, blunt steel implement, then let it float back up.

Does the float go down then float back up?

Yes: GO to «R4».

No, the float stays on the bottom of the brake master cylinder reservoir: REPLACE the brake master cylinder reservoir. BLEED the brake system. GO to «R9».

R4: CHECK CIRCUIT 531 (DG/Y) FOR GROUND SHORT

Key OFF.

Disconnect brake fluid level switch harness connector.

Disengage parking brake.

Check for ground short on Circuit 531 (DG/Y) at brake fluid level switch harness connector.

Is there a ground short?

Yes: REPAIR ground short in Circuit 531 (DG/Y). RECONNECT all components. GO to «R9».

No: GO to «R5».

R5: CHECK DIODE/RESISTOR ELEMENT

Engage parking brake.

Check for ground short on Circuit 531 (DG/Y) at brake fluid level switch harness connector.

Is there a ground short?

Yes: REPLACE resistor/diode element. RECONNECT all components. GO to «R9».

No: GO to «R6».

R6: CHECK CIRCUIT 512 FOR GROUND SHORT

Key OFF.

.

Disconnect fluid level switch.

Disconnect ignition switch (11572).

Disconnect anti-lock electronic control module.

Check for short to ground on Pin 2 of anti-lock electronic control module harness connector (Circuit 512 [LG]).

Is there a ground short?

Yes: REPAIR ground short in Circuit 512 (LG). RECONNECT all components. GO to «R9».

No: GO to «R7».

R7: CHECK IGNITION SWITCH

Reconnect ignition switch.

Check for short to ground on Pin 2 of anti-lock electronic control module harness connector (Circuit 512 [LG]).

Is there a ground short?

Yes: . RECONNECT all components. GO to «R9».

No: GO to «R8».

R8: CHECK BRAKE FLUID LEVEL SWITCH

Reconnect brake fluid level switch.

Check for short to ground on Pin 2 of anti-lock electronic control module harness connector (Circuit 512).

Is there a ground short?

Yes: REPLACE brake fluid level switch. RECONNECT all components. GO to «R9».

No: REPLACE anti-lock electronic control module. GO to «R9».

R9: CLEAR CODE/PULL CODE

Key OFF.

Reconnect battery negative cable.

Verify all connectors are installed.

Locate and disconnect the diagnostic connector from its mating half (Circuits 571 [BK/O] and 483 [R]).

Key ON.

Begin diagnostic trouble code flashout by grounding Circuit 571 (BK/O) for 1 second.

What code was retrieved?

DTC 16: GO to «Pinpoint Test S» .

DTC 12: If all steps are complete, GO to «Pinpoint Test T» . If all steps are not complete, RETURN to the last step completed and CONTINUE.

Different DTC: GO to pinpoint test for corresponding DTC.

 

yes if there is a short then you have a problem and need to replace the diode and I don't know where it is

 

1. RABS module-located in the dash under the instrument panel mount on a brace, center of panel area.
2. Dual Solenoid Electro-Hydraulic Valve is located 5 in. (127mm) rearward of the No. 1 crossmember on the inboard side of the LH frame rail.
3. Speed Sensor and Exciter Ring-located in the rear differential housing.
4. Yellow REAR ANTI-LOCK Warning Light-located in the instrument cluster.
5. RABS Diagnostic Connector (1991-96)-located on the main wire bundle inside of cab under the dash, slightly rearward driver side.
6. RABS Diagnostic Connector (1997)-located on the forward end of the power distribution box, under the hood.
7. Diode/Resistor Element (1991-96)-located three inches left of the cluster connector takeouts in the instrument panel wiring harness.
8. Diode/Resistor Element (1997)-located in the power distribution box, under the hood.
9. Sensor test Connector-located under the hood slightly rearward the washer bottle.

 

Where are you finding all the great diagrams?

 

It was on auto zone sign up for free and you get to use all the repair guides on the site, I was lucky to find it so i brought it here for future needs. I just wish I knew which one was the ABS diode . There are 4 in the power box. I bought 1. one has an on and off switch.. what is it for?

 

Hmm. I will look for a wiring diagram sometimes the have locations noted for each component.

 

1k ohm resistor + diode

 

I have a diode in spot 12 in the power distribution box and I have what may be a diode clipped to the side of the box

 

I have 6 that look the same 4 inside the power box and 2 outside the main power box with one of them that has a on and off switch on it.


I have moved all of them one spot except the one with on and off switched.

 

I think you may be looking at relays, not diodes.

 

What else is in there? i have fuses, and the large square relays for sure and a white looking part like a fuse but in hard plastic nothing else ..??
I will get a photo

 

ok i found the diode how do i test it? I can find one to replace it with.

 

Just ordered a new one. not sure but i hope it fixes this issue. I have my doubts........

 

What is a ground short? a ground that is grounded? that would be impossible to see...?? or is it no ground where there should be a ground???

 

Post a pic so we can see what you mean by 6. My power distribution box only has 1 diode in it