Post by Greg K on Mar 22, 2012 21:08:05 GMT -6
Dear fellow Aurora obsessives...
I’ve been putting my brain to the grindstone and service manuals to once and for all solve why my Traction Control and ABS warning lights have been coming on and off intermittently for a few months now.
I’ve tried to find a rhyme or reason. They’ve blinked on when I’ve started the car. They’ve stayed off for a day or two at a time. They’ve come on when I’ve been going up a hill, down a hill, driving level, turning either way. And even come on when I’ve been sitting still just idling outside the grocery store, with my foot nowhere near the brake pedal. My only sense is that they come on more when the engine’s hot than when it’s cold, for what it’s worth. There’s no bearing noise; my wheels turn smoothly.
I’ve hooked up my OBDII code reader and ... no codes. I’ve paid someone with a fancy-schmancy Tech II code reader that he paid a grand for – the kind that can see ABS codes – and it couldn’t draw any codes, either. (And this is when the lights were illuminated on my dash.) In fact, it wouldn’t even admit my car has an ABS system; it couldn’t see it at all. (That’s another question.... we’ll leave that for now.....)
I’ve read the 1997 Aurora and Riviera service manual, which states that low brake fluid, among other things, can cause both TC and ABS lights to illuminate without setting any codes.
I’ve combed the Net like a mad beggar to read frustrating horror story after gruesome wallet-busting tale of folks who have gone to dealerships, and worse, only to spend hundreds and thousands on replacing wheel hubs, EBCM’s (Electronic Brake & Traction Control Modules / the ABS computer) and BPMV’s (Brake Pressure Modulator Valve Assembly / the ABS pump). It seems everybody makes a quick best guess – then throws money at the problem. And – SURPRISE!!! – the problem comes right back on the drive home – the TC and ABS lights wink at you as if to say: SuCkEr!!!
For me, the joy of the Aurora hobby is learning about and understanding how these magnificent Oldsmobiles are designed and built, and doing as much of the work I can myself. (Over the years I’ve done this for my four Toronados — 1970 GT, 1981, 1987 and 1992 Trofeo — and it’s a great feeling to do it yourself and learn something new.)
So far I have, in what I consider a very logical order (trying to go from easiest to hardest), done the following
• Checked and cleaned the terminals on the 10A ABS fuse in the Instrument Panel fuse block (just inside the driver’s door cavity on edge of dashboard).
• Done the same for the two big ABS fuses – main and pump – under the hood in the fuse box behind the passenger side headlight along the fender.
• Checked brake fluid level and topped up. And cleaned, tested connection on multimeter and plugged back in the fluid level sensor on the brake fluid reservoir.
• I’ve pulled off all four wheels and contact-cleaned and WD40’d the sensor connector plugs on each wheel; not that any looked dirty or corroded at the time. (This is supposed to be the big one that solves the problem! Not for old Greggy here...)
• I’ve disconnected the EBCM connector from the EBCM/ABS computer (mounted on the strut pillar passenger side under the hood) and cleaned and tested its 55 pins. My car is minty under the hood, and there was no corrosion. Still, I used electrical contact cleaner and toothbrush to clean it spotless.
• I’ve measured the resistance/connection on the pins and wires that run to the fluid level sensor on the BPMV Assembly/ABS pump (located underneath the passenger headlight along the front frame rail).
• I’ve measured the resistance, using the EBCM connector plug female side, between grounds #1 and #19. My grounds are good.
• I’ve verified battery voltage on various connector plug circuits as requested by the service manual. Perfect.
• I determined which pairs of pin numbers on my EBCM connector plug run to the each sensor on each of my wheels. And first I measured the resistance to each sensor, and it came up perfect, almost exactly 1 Ohm for each of all four wheel sensors, when measured using the 2K Ohm scale on the multimeter.
• Now I wanted to see if the sensor was working when the wheels turned, and check all the wiring harnesses from each wheel to the EBCM as well. The service manual says to take off the wheel, disconnect the sensor and probe the sensor terminals to measure for alternating current (AC) while spinning the wheel. Sounded like too much work to me. So I jacked up each wheel, one at a time, and connected my multimeter to the two corresponding EBCM connector plug circuits for each wheel, and just spun the wheel by hand. Each wheel easily generated the 100 mV (millivolts) the manual says they should. So, it would appear my sensors, plugs, harnesses are all working fine, as they do generate current when spun.
MY THEORY:
A) I’m thinking the EBCM / ABS Computer has just gone twitchy – as the service manual says very clearly in Book 1 on Page 5E2-23 ABS/TCS that if I’ve tested all of the above and the EBCM connector appears free of corrosion or damage and appears to make good terminal contact when plugged in – then I should unequivocally replace the EBCM.
B) The fly in the ointment is the fact that the high-price Tech II code reader didn’t recognize my car as an ABS-equipped car. That may be hinting at another avenue to explore. On Page 8A – 50 – 10 Electrical Diagnosis in Book 2, when a scan tool does not communicate with a module – in my case the PCM (Powertrain Control Module; behind the glove compartment, which would store ABS codes, I believe), then I may have a suspect PCM. More to explore on this later, perhaps.
There is one quirky thing I have noticed, that you veterans of the ABS/TC wars may find significant: If I have my foot on the brake when I start the car, there is no shudder to the brake pedal at all when everything is working right; and the ABS/TC lights go out once the engine is running a second or two, as they should.
BUT ... when I start the car and there’s a shudder/kick from the brake pedal, I already know the lights are going to stay on, and they do. (And, no, I never start the car with my foot on any pedal as a habit; it just is something I’ve been doing to find out why the pedal shudders when I start it and the TC/ABS lights stay on.) And I do know that the ABS computer does a quick test pump of some sort whenever the car is started – it’s just that it’s harder/firmer when the TC/ABS lights are on.
I’m not about to pay $400 or $600 or more for new EBCM / ABS computer or BPMV / ABS pump, but I am now watching the local pick and pull for a 96-99 Aurora or Riviera to come in so I can pick up a used computer and slap it in for $50 or $60. I live in a city of a million people, so I know one will show up within a week or two, most likely.
And I’ve read the many excellent threads on this forum about this problem, and I thank you all. But this is a maddening problem, and most of the advice seems to be check harnesses, check sensors and swap in new wheel bearing hubs.
I WILL NOT SETTLE FOR SOLVING THIS BY SPENDING MONEY ON GUESSWORK! I want to know and understand this system. Yes it’s complicated, but what a fascinating hobby we have -- and I love it!
I haven’t totally solved my problem, but I’m just about there. I can almost smell success.
I wish I knew someone with a Aurora 96-99 here in Edmonton who would let me swap in their ABS computer for an hour or so to verify my diagnosis ... but that would be too much to hope for!
In any event, pardon my winder of a posting here, but I wanted to share with you what I’ve tested and eliminated so far, and to hear your thoughts as to what might be my next move. Jump in! I welcome any and all comments from the mighty Aurora brain trust. So jump in!
I hope you find this even mildly useful.
Yours in Aurora,
Greg “Dr K” Kennedy
I’ve been putting my brain to the grindstone and service manuals to once and for all solve why my Traction Control and ABS warning lights have been coming on and off intermittently for a few months now.
I’ve tried to find a rhyme or reason. They’ve blinked on when I’ve started the car. They’ve stayed off for a day or two at a time. They’ve come on when I’ve been going up a hill, down a hill, driving level, turning either way. And even come on when I’ve been sitting still just idling outside the grocery store, with my foot nowhere near the brake pedal. My only sense is that they come on more when the engine’s hot than when it’s cold, for what it’s worth. There’s no bearing noise; my wheels turn smoothly.
I’ve hooked up my OBDII code reader and ... no codes. I’ve paid someone with a fancy-schmancy Tech II code reader that he paid a grand for – the kind that can see ABS codes – and it couldn’t draw any codes, either. (And this is when the lights were illuminated on my dash.) In fact, it wouldn’t even admit my car has an ABS system; it couldn’t see it at all. (That’s another question.... we’ll leave that for now.....)
I’ve read the 1997 Aurora and Riviera service manual, which states that low brake fluid, among other things, can cause both TC and ABS lights to illuminate without setting any codes.
I’ve combed the Net like a mad beggar to read frustrating horror story after gruesome wallet-busting tale of folks who have gone to dealerships, and worse, only to spend hundreds and thousands on replacing wheel hubs, EBCM’s (Electronic Brake & Traction Control Modules / the ABS computer) and BPMV’s (Brake Pressure Modulator Valve Assembly / the ABS pump). It seems everybody makes a quick best guess – then throws money at the problem. And – SURPRISE!!! – the problem comes right back on the drive home – the TC and ABS lights wink at you as if to say: SuCkEr!!!
For me, the joy of the Aurora hobby is learning about and understanding how these magnificent Oldsmobiles are designed and built, and doing as much of the work I can myself. (Over the years I’ve done this for my four Toronados — 1970 GT, 1981, 1987 and 1992 Trofeo — and it’s a great feeling to do it yourself and learn something new.)
So far I have, in what I consider a very logical order (trying to go from easiest to hardest), done the following
• Checked and cleaned the terminals on the 10A ABS fuse in the Instrument Panel fuse block (just inside the driver’s door cavity on edge of dashboard).
• Done the same for the two big ABS fuses – main and pump – under the hood in the fuse box behind the passenger side headlight along the fender.
• Checked brake fluid level and topped up. And cleaned, tested connection on multimeter and plugged back in the fluid level sensor on the brake fluid reservoir.
• I’ve pulled off all four wheels and contact-cleaned and WD40’d the sensor connector plugs on each wheel; not that any looked dirty or corroded at the time. (This is supposed to be the big one that solves the problem! Not for old Greggy here...)
• I’ve disconnected the EBCM connector from the EBCM/ABS computer (mounted on the strut pillar passenger side under the hood) and cleaned and tested its 55 pins. My car is minty under the hood, and there was no corrosion. Still, I used electrical contact cleaner and toothbrush to clean it spotless.
• I’ve measured the resistance/connection on the pins and wires that run to the fluid level sensor on the BPMV Assembly/ABS pump (located underneath the passenger headlight along the front frame rail).
• I’ve measured the resistance, using the EBCM connector plug female side, between grounds #1 and #19. My grounds are good.
• I’ve verified battery voltage on various connector plug circuits as requested by the service manual. Perfect.
• I determined which pairs of pin numbers on my EBCM connector plug run to the each sensor on each of my wheels. And first I measured the resistance to each sensor, and it came up perfect, almost exactly 1 Ohm for each of all four wheel sensors, when measured using the 2K Ohm scale on the multimeter.
• Now I wanted to see if the sensor was working when the wheels turned, and check all the wiring harnesses from each wheel to the EBCM as well. The service manual says to take off the wheel, disconnect the sensor and probe the sensor terminals to measure for alternating current (AC) while spinning the wheel. Sounded like too much work to me. So I jacked up each wheel, one at a time, and connected my multimeter to the two corresponding EBCM connector plug circuits for each wheel, and just spun the wheel by hand. Each wheel easily generated the 100 mV (millivolts) the manual says they should. So, it would appear my sensors, plugs, harnesses are all working fine, as they do generate current when spun.
MY THEORY:
A) I’m thinking the EBCM / ABS Computer has just gone twitchy – as the service manual says very clearly in Book 1 on Page 5E2-23 ABS/TCS that if I’ve tested all of the above and the EBCM connector appears free of corrosion or damage and appears to make good terminal contact when plugged in – then I should unequivocally replace the EBCM.
B) The fly in the ointment is the fact that the high-price Tech II code reader didn’t recognize my car as an ABS-equipped car. That may be hinting at another avenue to explore. On Page 8A – 50 – 10 Electrical Diagnosis in Book 2, when a scan tool does not communicate with a module – in my case the PCM (Powertrain Control Module; behind the glove compartment, which would store ABS codes, I believe), then I may have a suspect PCM. More to explore on this later, perhaps.
There is one quirky thing I have noticed, that you veterans of the ABS/TC wars may find significant: If I have my foot on the brake when I start the car, there is no shudder to the brake pedal at all when everything is working right; and the ABS/TC lights go out once the engine is running a second or two, as they should.
BUT ... when I start the car and there’s a shudder/kick from the brake pedal, I already know the lights are going to stay on, and they do. (And, no, I never start the car with my foot on any pedal as a habit; it just is something I’ve been doing to find out why the pedal shudders when I start it and the TC/ABS lights stay on.) And I do know that the ABS computer does a quick test pump of some sort whenever the car is started – it’s just that it’s harder/firmer when the TC/ABS lights are on.
I’m not about to pay $400 or $600 or more for new EBCM / ABS computer or BPMV / ABS pump, but I am now watching the local pick and pull for a 96-99 Aurora or Riviera to come in so I can pick up a used computer and slap it in for $50 or $60. I live in a city of a million people, so I know one will show up within a week or two, most likely.
And I’ve read the many excellent threads on this forum about this problem, and I thank you all. But this is a maddening problem, and most of the advice seems to be check harnesses, check sensors and swap in new wheel bearing hubs.
I WILL NOT SETTLE FOR SOLVING THIS BY SPENDING MONEY ON GUESSWORK! I want to know and understand this system. Yes it’s complicated, but what a fascinating hobby we have -- and I love it!
I haven’t totally solved my problem, but I’m just about there. I can almost smell success.
I wish I knew someone with a Aurora 96-99 here in Edmonton who would let me swap in their ABS computer for an hour or so to verify my diagnosis ... but that would be too much to hope for!
In any event, pardon my winder of a posting here, but I wanted to share with you what I’ve tested and eliminated so far, and to hear your thoughts as to what might be my next move. Jump in! I welcome any and all comments from the mighty Aurora brain trust. So jump in!
I hope you find this even mildly useful.
Yours in Aurora,
Greg “Dr K” Kennedy
