Mechanics

ABS AND BRAKE LIGHT STAY ON

2001 Chevrolet Astro • 6 cylinder 2WD Automatic • 44,000 miles

I have a 2001 Astro van with 44000 miles. The other day the ABS light came on. After parking and turning the key off, then back on and driving, it would be off for about 30 minutes then back on again. Then the next day it came on along with the red brake light warning. I adjusted the rears, topped off the ms and topped off the power steering rez. It did not come on after that for a day. Now they are both back to on all the time. I have checked the entire system without finding anything out of whack. Any ideas?
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TheNightowl
April 15, 2011.



There will be at least one diagnostic fault code stored in the ABS computer. Having those codes read will get you into the right circuit or system.

The brake fluid shouldn't be filled. If it was excessively low, either there is a leak that must be addressed or the front disc brake pads are worn to the point of replacement. When you push the pistons back into the calipers to make room for the new pads, that fluid is going to overflow and make a mess.

Caradiodoc
Apr 15, 2011.
Could be caused by one of the following below

Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Crankshaft position sensor
Knock sensor
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking or defective fuel pump.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.

Note: If it doesn't apply disregard it and keep testing

Rasmataz
Apr 15, 2011.
Wrong question -sorry Doc cannot delete

Rasmataz
Apr 15, 2011.
No need to apologize. Since we lost the ability to delete our own replies, we're all posting all over each other. I don't bother to apologize anymore and I don't expect any in return. I'm not offended when other people add their thoughts. It's just the nature of this new format.

Have a dandy, ... Uhm, ... Lets see; what day is it? Oh, have a dandy Friday!

Caradiodoc
Apr 15, 2011.
I finally got the code read, and it says co265 ebcm malfunction. The problem with that is I can find hardly any info on what values to check for. They are tight-lipped in my area and I had to pull teeth to get a free read. What I have done so far since the read, is cleaned the front wheel sensors. Even the backside of the sensor mount, checked all conectors, and made sure power is at the module.

I did notice that both the module/pump and sensor wiring is too close to the exhaust IMO. I also notice the lights come on when its hot under there. In the mornings they're off until I get some mileage, then if I let it sit and cool down, the lights are off on restart. Go back to driving for a bit, lights back on. Maybe. Yesterday was cool and real windy and the lights stayed off until it sat inside for 20 minutes, then back on until the next restart.

The replacement module is $1124.26 ! And I don't even know if thats the culprit. Should I try to get the code read while the error lights are on?
Is there a way to make the pump work without finding a dirt road to where I can hear it kick in while the error lights are off?

I know this is not a serious problem, but its driving me nuts and I have to figure it out.

The only change I have done is hauling much more weight in the last 3 months, and just before this went wacky I started smelling the nice rotten egg smell from the cat. Thats why I'm leaning toward a heat related problem. I doubt its the speed sensor in the tail end of the trans, and the brakelight switch seems a bit out there too.

Tiny
TheNightowl
Apr 27, 2011.
Edit: Rotten egg smell ALONG with hearing the exhaust popping and cracking while cooling down which I have not noticed before.

Tiny
TheNightowl
Apr 27, 2011.
I've seen controller codes before when the system was working fine otherwise, so I wouldn't jump at the module just yet. The heat issue is one possibility but rather than looking at wires, it's more likely to affect electronic circuitry such as the computer. Heat-related problems were half of what I used to search for when fixing tvs.

Something else to consider is that eventually an electrical problem will be detected during the self-test when you start the engine. If the hot exhaust is causing wires to melt, that is going to continue to get worse and the problem will be detected sooner than after a half hour.

Something else to look at is the tone rings by the two front wheels. If one is cracked, that won't be detected until after the vehicle is moving. At first the extra pulse from the crack might be rationalized as the vehicle is going around a sweeping curve, but eventually the computer will realize there's a mismatched wheel speed and will turn on the light. The memorized code will be different than what you're getting, but there are conditions that must be met for any code to set. One of those conditions is that certain other codes are not already in memory. The computer compares many things to determine when there is a problem, and if the things it's comparing something TO has a problem, it knows it can't use that to test something else. For that reason, sometimes a new fault code will show up right after the previous one was repaired.

Now that I confused you with all of that, I'm inclined to think something inside the computer is getting warm and causing the internal fault. GM has a real high failure rate of the ABS computers on the trucks but I haven't heard of that on the Astro Vans. Also, that applies to the four-wheel systems, not rear-wheel systems.

Before you spend that kind of money for a computer, you should consider finding one at the "pick-your-own-parts" salvage yards. If you're between Indianapolis, Ohio, and southern Georgia / Alabama, there is a chain of very clean and well-organized yards and the parts are very inexpensive. With a warranty you can expect it to run around 50 bucks.

Caradiodoc
Apr 27, 2011.
Today I cleaned and made sure all the grounds I could find were secure. Drove it for a bit and the lights were off. I connected a volt meter to the front wheel sensor leads and got 2.65 volts on each wheel sensor seperately and that was by turning each wheel at a somewhat fast constant speed to make it easier. If I tried the one rev per second deal it was hard to get a good read. From what I have read, the voltage should be a minimum of 350 acmv's, but my tester doesn't do milli so I had it on normal scale ac. Then I drove it again. Lights still off.
I unplugged the wheel sensor connector and started it up. Immediately had both lights on. Plugged them back in, started it up, both lights went off, so I have to assume the front sensors are fine. I did the same thing with the sensor on the tail end of the trans. Same results so I have to assume that sensor is also fine.

Then I drove about 4 miles and parked it while the lights were still off. Got back in 15 minutes later and both lights were on. I drove another 7 miles and shut it off. Got back in maybe 10 minutes later and the lights were off all the way back home which was another 7 miles.

My next test will be while the lights are off. I will brake hard on a dirt road and see if the pump kicks in. If it does? If it does not, then would the pump be faulty? Notice I'm staying away from the module until the last resort!

Tiny
TheNightowl
May 1, 2011.
Now I have to defer to my Chrysler experience but even then I didn't work on their systems very often. Pulling a connector, as you found out, is detected as an open electrical circuit during the six-second self-test when you turn on the ignition switch. All you can be sure of when the warning lights do not turn on right after that self test is the electrical circuit has continuity. If the air gap is wrong, the tone ring is cracked or missing, or there's a problem with the sensor's magnetic core, that won't be detected until the van is moving and the computer sees the signals from the other sensors.

Here is where I see a potential problem. On some vehicles the ABS computer can only store one diagnostic fault code. There might be one in your computer now from the first time the warning light turned on. On some of those older systems the codes do not self erase after a certain period of time if the problem doesn't return. They have to be erased with a scanner, and until it is, the computer can't set a new code when necessary. The frustrating part of this system is that when the first problem is corrected and the code is erased, the computer is able to set the next code and turn the warning light on again. Now you have what appears to be a new problem and it's often blamed on the mechanic who performed the first repair. That can go on and on if there are multiple problems. This rarely happens when you take the vehicle in right after the light comes on because that second or third problem hasn't had time to develop yet. It happens more often when people ignore the warning light for months or years.

More advanced computers can store multiple codes. Being a three-channel system, I suspect this pertains to your van. The thing to be aware of is there is always a set of conditions that must be met for a code to set. One of those conditions is that certain other codes are NOT in memory already. As an example, the computer will not set a code for mismatched wheel speeds if there is already a code for loss of signal from one sensor. It knows it has no reliable signal to compare to so it won't set that code. Likewise, you are going to have three codes related to open circuits to the sensors you unplugged. Even though the light is off now, those codes are still in memory. I don't know what will happen with any new problems that are detected. They might be recorded when everything else is working, or they might be ignored because of the existing stored codes.

The place to start, if you have access to a scanner, is to read and record all of the stored codes, then erase them and drive it until the light comes back on, then read them again. If you come up with a list of codes, you should be able to figure out which ones were set from unplugging sensors. Those can be ignored.

Another thing to consider, which I would never recommend for 2002 and newer vehicles, is to disconnect the battery cable for a minute to try to erase the codes. Some vehicles can not have their codes erased that way. Even unplugging the computer will still keep the codes stored. Those must be erased with a scanner. If yours DO erase, there will only be the one current code if you drive it until the light comes back on.

Caradiodoc
May 1, 2011.
When I pulled the rotors I cleaned inbetween each grove on the tone rings and never noticed any cracks. The only thing I did notice was that the rings were quite shiny from turning? Against the sensor's mounting face. Also, the mounting surface was not worn in any bad way to effect anything, the shine was probably due to crud between the 2. If there were any cracks they should? Have been easily noticable because of the crud that would have built up in the crack. Now that I said that, and along with the heat issue I believe might be the problem, it IS possible there may be a crack that only appears when that ring gets hot and expands. I didn't like the construction of the sensor and it's flimsy mounting process either. The rubbing was slight and there was a small amount of crud behind the mounting face that I assume caused the rub in the first place. Either that or the boys in mexico placed both rings too far out, but if that were the case it should have left the factory with the code already set?

I feel like an idjit for not asking the guy who scanned it to erase the code!

I will try to get him to erase the code/s sometime this week, and start from the beginning if the code sets again.

Tiny
TheNightowl
May 1, 2011.
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