FAQ: Anti-Lock Brakes and/or Traction Control Light/Lamp On

Probably a bad wheel speed sensor, although that usually triggers the ABS light too. Does the ABS work? Does the ABS light come on during the dash light test? (key-on)

I'll have to try out the ABS. The light does come on when during the light test.

I took it out tonight and found some slick roads to try it on. Yes, the ABS does work just fine

I believe our Riv had this problem after installing all new brake lines. If I recall, additional brake bleeding was needed to solve the issue. It was a few years ago so i'm not 100% certain that it was the same issue you are having. Just a thought.

One thing that worked for me is just pushing in the TC connector in the engine bay. Haven't had the light come on since.

I hope its as simple as the connection. Hopefully the rain will stop so I can try that

Where is this connector in the engine bay?

moldymac wrote:

I took it out tonight and found some slick roads to try it on. Yes, the ABS does work just fine

good, that rules out a wheel speed sensor.

Tried cleaning that connector under the hood, no change.

ok i know its been forever... but i finally got new wheel hubs installed. timken of coarse. my ABS/traction light is no longer on but it still makes a whining noise randomly when i take of, going slow or WOT. but just for a second. and still bad gas milage. whats next?

Stupid question, but what is your tire pressure? I run ~31 PSI. And as Deekster said, check for a dragging brake. I had that problem (wonder if it's a '96 specific issue?). I basically have the same mods as you and I get 16-18 with about half and half city/highway while driving somewhat hard.

35 psi, just got new brakes and rotors, done checked everything i know of.

crstump wrote:

ok i know its been forever... but i finally got new wheel hubs installed. timken of coarse. my ABS/traction light is no longer on but it still makes a whining noise randomly when i take of, going slow or WOT. but just for a second. and still bad gas milage. whats next?

OK I think we said we would tackle the bearings first, which you did. Now it's time for the MPG issue.

First question - find a stretch of highway that is not busy and we (the royal "we" - meaning You) will do some cruising.

Without being a safety hazard to yourself or others, using the cruise control drive at 55 MPH and note the RPM indicated on the tach.

Then drive at 65 MPH and note the RPM on the tach.

Report back the RPMs at those speeds and we'll take it from there. Again be sure to use the cruise control for these speed checks. IIRC the PCM meters fuel and manages the transmission differently if it thinks you might accelerate or something. It does not think that if you are using the cruise.

By the way the Riv does not get stellar city or city/suburban mileage.

Albertj

1500 RPM at 55 mph, 1800 RPM at 65. also forgot to mention the gas milage SLOWLY decreased, it didnt just suddenly drop from 21 to 14, its even been at 12 before. probably took about 2 months for it to stop dropping.

crstump wrote:

1500 RPM at 55 mph, 1800 RPM at 65. also forgot to mention the gas milage SLOWLY decreased, it didnt just suddenly drop from 21 to 14, its even been at 12 before. probably took about 2 months for it to stop dropping.

Cruise rims sound about right, someone else can verify.

12 mpg is not unusual for stop and go driving, Riv uses a lot of fuel at idle and in low gear, it is crammed to make a lot of power at low revs and that costs you city mpg big time.

Anyway...

Next question, what kind of fuel do you use, regular? Premium? One brand or any?

Question after that, how do you calculate your mpg? Using gas gauge? Measuring fuel use over measured miles? That is, just tell us how you tally mpg.

Question after that is, are you doing mostly city driving below say 45 mph?

93 octane, id say about 75 to 90% of time time its shell gas, i fill the tank up, drive it then fill it up again then do the math with miles and gallons, and yes, the city driving is right but iv always had same driving habits since iv got the car and i was getting 21 mpg, city. im trying pretty hard to keep my foot out of the gas for this tank to see if it helps. im goin on a 6hr trip in june, nothing but interstate so that should deff tell me if its just the city stop/go traffic or not.

crstump wrote:

93 octane, id say about 75 to 90% of time time its shell gas, i fill the tank up, drive it then fill it up again then do the math with miles and gallons, and yes, the city driving is right but iv always had same driving habits since iv got the car and i was getting 21 mpg, city. im trying pretty hard to keep my foot out of the gas for this tank to see if it helps. im goin on a 6hr trip in june, nothing but interstate so that should deff tell me if its just the city stop/go traffic or not.

My initial thought are you might be able to improve around-town mileage by resetting the PCM to factory defaults. I think this can be done by disconnecting the battery under the back seat for a while (I have heard that if you put the neg and positive terminals together it will speed up the reset by draining some sort of power reserve but I have no idea if that is true so unless you know for sure, don't do that).

Here are some further thoughts:

• When you drive the car it makes some adjustments to engine and transmission control on a rolling basis depending on how you drive. SO -- if you do stuff like "race to stoplights" your gas mileage will get much worse overall. Why? Because the PCM will force the car to stay in "power enrichment mode" and increase the amount of fuel used by entering Open Loop operation and increasing injector pulse width in order to prevent hesitation during acceleration.
  
  If you do not use cruise on the highway or you are cruising faster than ~55 your highway mileage will in all likelihood be worse than the published 27 MPG. Although I don't think the roll-off is all that big at 65. I think I heard it's like 24-5 at 70 and worse at 80.
  
  make sure your air cleaner element is clean
  
  If your fuel filter has not been changed in 50,000 miles you're (over) due. Gas is pretty clean nowadays so it may be not an issue at all. However if there was ever an anomaly - silt or condensation in the tank? - you'd have a little problem.
  
  make sure the plugs are clean and gapped properly - see the spark plug color pages in any Haynes manual for more on this
  
  make sure the wheels are aligned properly, if it is way out of wack you'll take a hit in MPG due to friction losses, not to mention tire wear
  
  even when aligned right your tires can cost you 1-2 MPG dep. on design and composition

Best way to check out MPG might be to hook a scanner to your car and read out the real time MPG. Car is capable of this but the interior designers omitted the user interface to the computers (it is installed in the Aurora, the Riv's 4-door G-platform partner). You can then go for a ride and log the MPG readout in real time on how fast you are going as a function of calculated distance and measured fuel usage. You'll need a Tech II, AutoTap, Car-Code or other scanner, not a code reader.

It might also be your injectors need cleaning so that their flow matches and they don't dump fuel.

For those of you wanting a more technical explanation: Over time the PCM will adjust long term fuel trim by putting a % bias against the fuel map tables. The LT trim can vary between -23% to +16%. If fuel trim goes + any significant percentage your gas mileage will decrease because the PCM will widen the injector pulse width. In practice it will widen it to the point where the worst fuel injector will operate OK. That's done basically by increasing pulse width until the sensors quit complaining e.g. the knock sensor. In this case I would use a scan tool to see if LT fuel trim was pegged at any positive value. IF so then I'd go looking for why. I would be checking for things like lazy oxygen sensors and such, because the oxy sensor is the main signal used to manage short term fuel trim. if oxy gets lazy and stays below about 450mV it will cause the car to tun a bit rich (indicating a too-lean condition when that is not really the case). The ST fuel trim can vary between -11 and +20%. SO if you have a lead foot, and a weak oxy sensor, the car will run rich all the time and combined with the adaptive transmission behavior and the ST/LT fuel trim the gas mileage will go down.

I would also check the knock sensor and its wiring. I would command a canister purge cycle and see that the EVAP system is running right. I would clean or replace the MAF sensor.

So -- what can you tell us about alignment, and the air cleaner? Can you try resetting the engine and transmission controls by disconnecting the battery for a while (and can someone else post how long that should be - I think an hour but I don't remember, so before you do it let's see if someone else knows and posts it)? Is your air cleaner clean? Have you pulled all the spark plugs one by one and checked gap (it's supposed to be .060 in and should be set dead on, not wider or narrower)?

My wild guess based on your posts so far is you have deferred maintenance to catch up on in the car, and you have a "lead foot." My further guess is there may be some other problem and we have not found it yet.

Long post.  Newbie on this forum.  

My 62-year old nere-do-well brother owns a 1996 Riviera 3800 supercharged version that he bought new.  He loves this car more than life itself, but is not financially stable nor is he a good auto mechanic.  The car is black with gray leather interior and the rosewood trim and has 106K miles.  Because of bad plug wires, the car sat, outside, for 2 years because it was cutting out so badly.   My neighbor had a 1993 GMC 4x4 1500 with 60K miles on it, so I bought that truck and traded it to my brother for the Riviera.  The last time I was over to see him, I trailered the car back to my house in Huntsville, Alabama, to get it running again so it could be sold rather than scrapped.    It was at this time that I learned that he loved that Riviera.

I, on the other hand, am a very good auto mechanic and I am ok financially.  Rather than sell the car, I decided to go completely through the car and fix everything and give it back to my brother as a surprise birthday present.  I have now been working on the car for the past 60 days and have replaced the following:  New hubs all around (Timken), disassembled the calipers and brackets and had them powder coated and rebuilt, new tires, new aluminum rims, new Brembo drilled rotors, new Akebono ProAct ceramic pads, new AC Delco water pump, new Iridium plugs, new AC Delco plug wires, rebuilt the Eaton M90 Supercharger and upgraded to a 3.6 aluminum pulley, new serpentine belts, new pulleys for the belts, new AC Delco camshaft position sensor, removed and had the OEM factory radio rebuilt, replaced the power radio antenna with a new AC Delco antenna, had the front seats re-leathered, restored the driver's door panel, and took the car to Birmingham to have it re-painted (the black paint and clear-coat had a bad case of the dreaded GM paint disease on the hood, top, and rear deck).  Total so far was just over $5K.  

All has gone well with the exception of fixing the Traction Control Off light.  I took the car to the dealer and had the codes pulled, and they said that both the EBTCM and the ABS Hydraulic Valve Modulator (AC Delco Part Number 25653461) were bad.  Just to make sure it was not a wheel speed sensor, I replaced all of the hubs.  Was not that.  I was able to locate a NOS EBTCM new in the box for $150, but that did not get it either.  I did extensive research for the valve modulator and none could be found.  Not only that, all ABS module repair places stated the units were unrepairable (or that replacement parts were unavailable).  I spent weeks calling around.  One guy even stated he had a NOS one in his garage he would sell for $1,400 but when he went to look for it he could not find it.  Stuff like this bothers me but I ordered one off Ebay from a salvage yard.  Put it on and the light would not go off.  Had the codes pulled again and the unit was bad.  Got a replacement unit and it was bad as well according to the dealer.  

Finally contacted a place in Tennessee who rebuilds modules.  Automotive Scientific, Inc.  Even though their www site indicated they did not service that unit, I called them anyway and talked with one of the technicians, who said he would take another look at that particular unit.  Two days later he called back and said that they could rebuild the 25653461 assembly (with Traction Control) and would offer a lifetime warranty (interpreted by them as a 13-year warranty).  The price was $325 plus shipping plus core.  I received the rebuilt unit yesterday but the car is being painted and I have noit been able to install yet.  At any rate I thought I would post this information for those of you out there in a similar situation who thought the only alternatives were to take out the TC bulb or go to a salvage yard.

Their contact information is toll free 866-983-6688.  I will post after installation and let you know how it went.  Pics to follow when it comes back from the painter.

Thanks a lot. Mine's been coming on a lot more recently. Can we get pics of the car? It has to look MINT with all of that work.

Welcome to the site.  

For starters, simply saying that the dealer said those parts were bad, and then going and replacing ALL of the hubs for no reason (which was stupid because you'd have an ABS light as well), and then not telling us what codes were in the vehicle doesn't help anybody. Did anybody check for a bad wire? Maybe a UART data line is corroded or broken? That might explain why 2 used units you've replaced were "bad". It's very uncommon for the EBTCM AND the Modulator to fail at the same time.

Was it any of these codes?

P1571 Traction Control Torque Request Circuit
P1573 Lost Communication with Brake/Traction Control System
P1653 Traction Control Delivered Torque Output Circuit

Could you get 2 failed used parts? Yes. Likely? No. I hope your rebuilt fixes your problem.

Sorry if I sound like a dick, but your post is misleading.

Welcome! That's awesome that you are going through all that for your bro. Good work!

Let us know if you have any questions. We've all been through most of the repairs you are describing. The supercharger probably didn't need to be rebuilt, but if it was noisy (clattery) most likely just the coupler in the snout needed to be replaced.

Also, be careful about the 3.6 pulley - make sure he will only run premium gas in it!!! If possible, connect a scanner that can show you the KR parameter and make sure it isn't too high.

When I first got the car running after changing the plugs and wires, I noticed two distinctly different sounds while driving.  The first was very accurately described by others on this forum as "rocks in a tin can" while at idle and under very low rpms.  I concluded it was probably the coupler in the supercharger so I ordered the kit with all of the bearings and such.  The kit took care of the nose, but did not cover the rotor pack needle bearings at the other end.  So I got those and whatever else I needed.  The second noise was while underway, and was a roaring sound from what seemed like both the front and rear.  I took one front hub off and it was trashed (excessive play), possibly while sitting for 2 years in Louisiana.  Also, one of the rear hubs was missing 2 lug nuts as the studs had been bent when the jack fell while the wheel was off.  That rear hub was also funky with much resistance while turning, so it got replaced.  Once in there, I elected to replace all hubs to start off at a good departure point.  After changing the coupler and the hubs, the car runs quiet except for just a bit more SC whine - which I like.

The forum write-ups on the spark plug replacement and the serpentine belts and water pump replacement were excellent and saved me a ton of effort.  My arms were still cut to ribbons on the bastard plug number 6, and I still curse the GM engineers on having to remove the motor mount and bracket to get to the belts (which lead to the water pump replacement while I was in there), but I've taken a liking to the old girl and gone out of my way to keep her going for my brother for another 10 years.  He ain't worth much, but he is the only brother I've got.

Only 93 octane gas has ever been used in the car since new, so that is not an issue.

Will post pics when I get her back from the paint shop in Birmingham.  I still have to put on the calipers, rotors, pads and wheels, so she should really look good once finished.

And Scott:  Yea, you did come off a little like a dick but I did not want to go into too much more detail in the initial thread since it was already longish.  No, I am not stupid, but spending a couple hundred and change more for 2 hubs and a water pump was worth it to me as my time to do such labor was limited and I don't like to do things twice.  The codes were on the service report form and I do not have it with me so I did not list them.  No hard feelings as the losses we experienced in the War of Northern Aggression have been recovered since, and more.

  The missing info! It just sounded like you replaced stuff for no reason. I'm glad you decided to resurrect the car rather than scrap it. Nothing worse than a Riv going to the yard...

I want to know which codes were in the car. It might just be something simple to fix your problem.
Yes, I'm a dick, but I'm here to help  

P.S. I thought it was "Southern Aggression?"

Got the car back from the body shop and installed the rebuilt hydraulic valve modulator. Installed the drilled rotors and the powder coated calipers, then bled the brakes. Mounted the new wheels and took her for a drive. All idiot lights now off and for the first time I heard the hydraulic pump cycling away for a few seconds. Spun the tires and locked the brakes and both the Traction Control and ABS functions have been restored. The car really really looks and drives great. I took some pictures but have not yet figured out how to post them. $325 for a rebuilt hydraulic valve modulator with a 13-year warranty was worth every penny spent.

upload them on your photobucket acct then copy and paste the image link