ABS issues and relay questions...

joenintiesc

Registered User
I've spent awhile searching through the forum, but I still have a question or two - first the background:

  • 1990 SC with Cobra brakes and later year spindles
  • ABS light has always been on but brakes have always worked great (just w/o ABS), removed ABS light a long time ago.
  • Car not driven very often over the last several years. Seemed to be a slow leak of brake fluid, as every time I did drive it the red brake light would randomly turn on and off until I added brake fluid to bring back to proper level.
  • Accumulator replaced about 10 years ago, but less than 20k miles on it.

Now I have the hard brake pedal and braking is severely reduced, red brake light on constantly. I don't think the pump is running at all.

I pulled the ABS relay, cleaned it with electrical cleaner - no change. Fuses look good. Ignition switch in steering column was acting up - replaced it but no change in brake issue.

So I replaced the ABS relay with one from Advance Auto, listed as:
BWD ABS Warning Lamp Relay, Part No R649P
This is the gray one, not the more expensive brown one.

It fits - that means it should work, correct?

Also, I came across this info from this article: http://www.albeedigital.com/supercoupe/articles/abs-system.html:

For all applicable model years the Anti-Lock Power Relay and the Hydraulic Pump Motor Relay are located on the passenger side firewall area. When facing the engine bay these relays are located as follows:

90 Model Year (Left to Right) WOT AC Cutout Relay, Hydraulic Pump Motor Relay, Anti-Lock Power Relay


The description above makes it sound like there are TWO relays that are associated with the ABS unit - but I only see two on the firewall in total, and I assumed the other was the WOT relay. Am I missing something here?

I would really like to be able to fix this without pulling the unit - if the relay is not the issue can I test the motor/ pump without removing it? If the pressure switch in the unit is bad - can it be replaced while the ABS unit is in the car?

Any help and assistance would be greatly appreciated!!
 
There is a pressure switch on the ABS unit itself that drives the relay.. best thing is to check that the relay is energized when you first turn the key on. You don't need to start the engine for this. You should have power to the relay (pull it out and check that you've go the right pins) and hear the motor run. If not happening, you'll just have to go into problem trace mode.. I'd say chances are 3/4 that the pressure switch has failed. You can further test it on the car, but its beyond for me to describe it. Do a search for Duffy's writeup on the Teves II.

You can't easily replace it with the unit in the car, but removing the Teves unit it is not all that horrendous.
 
Last edited:
So I replaced the ABS relay with one from Advance Auto, listed as:
BWD ABS Warning Lamp Relay, Part No R649P
This is the gray one, not the more expensive brown one.

It fits - that means it should work, correct?

Yes and no. Check the pin labels on the bottom (if present). Make sure you have the same number of pins and your numbers are in the same place. (87, 30, etc.) There are also differences like latching relays, switched-on vs. switched-off, etc., but I think this is a normal relay.

Also, I came across this info from this article: http://www.albeedigital.com/supercoupe/articles/abs-system.html:

For all applicable model years the Anti-Lock Power Relay and the Hydraulic Pump Motor Relay are located on the passenger side firewall area. When facing the engine bay these relays are located as follows:

90 Model Year (Left to Right) WOT AC Cutout Relay, Hydraulic Pump Motor Relay, Anti-Lock Power Relay


The description above makes it sound like there are TWO relays that are associated with the ABS unit - but I only see two on the firewall in total, and I assumed the other was the WOT relay. Am I missing something here?

I would really like to be able to fix this without pulling the unit - if the relay is not the issue can I test the motor/ pump without removing it? If the pressure switch in the unit is bad - can it be replaced while the ABS unit is in the car?

Any help and assistance would be greatly appreciated!!

I think that there are two relays - one for the pump motor and one for the ABS controller and solenoids and what not.

I think the one that controls the pump is the expensive brown one. Possibly a 5-pin instead of a 4-pin?

You may have a pressure switch problem, but you need a functioning relay to diagnose it.

Also put your ABS warning light back in when you can. It could help you sniff out a problem ahead of time. I am pretty sure that the later model ABS sensors can be adapted to the early harness and controller, but you may need to check the placement of the tone rings relative to the sensor heads.

As for checking the pump and motor, yes, you can. Disconnect the round 4-pin motor plug that is alongside the master cylinder, and use jumper wires (preferably fused and of equally heavy gauge as the harness wires) to apply power and ground to one red and one gray wire. (Both red do the same thing, and both gray do the same thing, though which color is power may have switched by year. If the connections are reversed, the motor will run, but the pump won't build pressure.)

Bad pressure switch is a common failure at this age. Still available new. Fairly easily diagnosed with multimeter and logic. Worn out motor brushes is another common problem. Motor is rebuildable. Pump failure a little less common, and a little harder to fix.
 
My 91 SC did the same thing a couple years ago with the hard pedal, severe loss of brake performance brake light and ABS light on the dash. While trouble shooting it I determined that the relay was supplying power to the pump when the ignition was turned on, but discovered the pump would only run for about half a second before shutting off.

Ended up being a bad relay (the brown one). Relay was switching power to the pump but would not hold the electrical load and dropped out after half a second.

David
 
Thanks for the responses! So far I've been working on this by myself, and so it's been impossible to listen at a good vantage point for clicking and pumping sounds from inside the car while turning the key. Hopefully tomorrow the wife will be able to turn the key while I have my ear closer to the relay and MC.

I just want to completely rule out an easily solvable electrical issue before committing to pulling the MC out, and then facing the more difficult choice of whether to replace with same expensive Teves II, or downgrade to non-ABS.

That said, if I pull off the relay and supply 12 volts to the female end of the connector, I should be able to make the pump run if it is operable? Or do I have to do that on the unit itself?
 
Yes and no. Check the pin labels on the bottom (if present). Make sure you have the same number of pins and your numbers are in the same place. (87, 30, etc.) There are also differences like latching relays, switched-on vs. switched-off, etc., but I think this is a normal relay.

I'll check it again, but I know it has the same # of pins.

I think that there are two relays - one for the pump motor and one for the ABS controller and solenoids and what not.

I think the one that controls the pump is the expensive brown one. Possibly a 5-pin instead of a 4-pin?

Yes, the one on the passenger firewall is 5 pin relay.

You may have a pressure switch problem, but you need a functioning relay to diagnose it.

Also put your ABS warning light back in when you can. It could help you sniff out a problem ahead of time. I am pretty sure that the later model ABS sensors can be adapted to the early harness and controller, but you may need to check the placement of the tone rings relative to the sensor heads.

I don't think it would help - the light has always just stayed on continuously. I think I remember it being an ABS wheel sensor issue, but when I upgraded the spindles I couldn't find new sensors, so currently there aren't even any front abs wheels sensors installed... I guess if I eventually put the sensors back I will put the light back in

As for checking the pump and motor, yes, you can. Disconnect the round 4-pin motor plug that is alongside the master cylinder, and use jumper wires (preferably fused and of equally heavy gauge as the harness wires) to apply power and ground to one red and one gray wire. (Both red do the same thing, and both gray do the same thing, though which color is power may have switched by year. If the connections are reversed, the motor will run, but the pump won't build pressure.)

Ok, I guess this is not doable via the relay connector then

Bad pressure switch is a common failure at this age. Still available new. Fairly easily diagnosed with multimeter and logic. Worn out motor brushes is another common problem. Motor is rebuildable. Pump failure a little less common, and a little harder to fix.

If I have to pull the MS to replace the pressure switch, I am going to just either convert to non-ABS, or go with a completely rebuilt Teves II.
 
My 91 SC did the same thing a couple years ago with the hard pedal, severe loss of brake performance brake light and ABS light on the dash. While trouble shooting it I determined that the relay was supplying power to the pump when the ignition was turned on, but discovered the pump would only run for about half a second before shutting off.

Ended up being a bad relay (the brown one). Relay was switching power to the pump but would not hold the electrical load and dropped out after half a second.

David

Lol - I came across your old thread and when I read the last post by you I thought "please let it be that simple for me too!!!"
 
The front sensors for the later cars are still available new, though they are expensive.

STANDARD MOTOR PRODUCTS Part # ALS500 {#F3LY2C204B, F3LY2C204BA}
Front Left

STANDARD MOTOR PRODUCTS Part # ALS502 {#F3LY2C204A, F6SZ2C204AB}
Front Right

RockAuto has them. They are also sold under Raybestos and Airtex brands, though with different part numbers.

They have been retrofit to older Thunderbirds in the past.

http://www.sccoa.com/forums/showthread.php?t=57882&highlight=abs+wheel+sensor+connector

So that could get your ABS working again.

...

However, you have more pressing problems.

Hmm, I think you can actually jump the pins at the relay and test the motor. One side of the relay connector is run by the pressure switch and/or computer, and the other should be power direct to the motor. So if you are already working in that area, go ahead and try it.
 
abs

Thank you for the info! :)

I had the same thing on my 90 sc. replaced the brake pressure swtich problem solved. also u have have to check ur wheel sensors one of the could be broken. fronts were $65 @.I should have checked in my garage first where I had 2 fronts in nice shape. smh.grrrrrrrr:mad:
 
I had the same thing on my 90 sc. replaced the brake pressure swtich problem solved. also u have have to check ur wheel sensors one of the could be broken. fronts were $65 @.I should have checked in my garage first where I had 2 fronts in nice shape. smh.grrrrrrrr:mad:

Did you have to pull the unit out of the car to replace the pressure switch?
 
618-309-3305 is my cell. I just went through this with mine. Give me a call tomorrow and I will walk you through the testing. You can easily remove the pump without taking the whole master cylinder unit out. Fifteen minutes I can have one out.
 
abs

Did you have to pull the unit out of the car to replace the pressure switch?
I have a friend who works for the ford dealer and he owns a sc himself.on the t-birds there is a 3inch hole where a skinny 36mm socket can fit the switch. it's on the drivers front wheel well on the right side of the upper control arm. u will have to remove the plastic cover,u also need to put a 2inch by 2 inch piece of wood underneath the abs unit so when I turn it it won't flex breaking the one of the bolts that hold the pump motor. took me 15 mins with the right tool.
 
Back
Top