99 WJ Grandy ABS light on

[knudsen]

I got the light a few days ago. On start up, I get no light, but I get three beeps, a short pause and three more. No OBD codes (Tried key on-off-on-off-on as well as a mactools obdII scanner. As soon as I hit 10 MPH, another longer beep and the light comes on and stays on until key off. I don't think ABS is working after the light comes on, but a few times before the light 10 mph, it ABS'd as I was doing a normal stop on dry pavement.

I went one size up on tires a few months ago, but no problems at all with ABS or anything until now. I did check the pressure and in fact dropped them all by 3 PSI to see if a little smaller diameter would help. I might do the math on the size different and lower them a little more. I just don't know why the newer tires would be OK for 2000 miles or so. I put them on before our first snow storm, which did come early.I've heard larger tires can be a problem, but not to this particular model. I did check fluid.

Rainy day just before it happened, but didn't hit any water hard or anything. Wheel sensors look intact and I reseated the big plug on the pump/CPU thingy.

Dambid Haynes says to take it to the dealer. Doh! :x

Any ideas?

Note: I'm dropping this on a couple of forums, because I haven't found anything on Google or searching the forums I'm posting on. Hope it's not annoying the multi-forum readers.

 

[SteelHeadz]

If you still have access to that Matco Scanner, see if it's capable of monitoring the Wheel speed sensors. Your description of the symptom seems to point towards a Speed sensor not reading the wheel speed. Another thing to consider is how much larger tires did you install compared to the stock. If it's a considerable amount, it would confuse both the PCM and TCM from the output speed on the Transfercase sensor vs. speed from the wheel sensors.

 

[knudsen]

Thanks, Mikey.

I went from P225 75R16 to P245 70R16, so in plain English, it's a whole .2 inches taller, now 29.5" dia. Before investigating that, I aired them on down to 24 PSI and went out and it acted a little different. We got a little snow so I could test ABS and it does pulse some, but it's not near as good as it was. I can get them to skid now. No more beeps, and the light does not come on all the time.

Haynes says I need a DRB scanner tool, what ever that is. I think I'm gunna put that Haynes in the can and use it for toilet paper.

Scanner I have is a 9040 and the book says it can scan all global (generic) obd II codes.It can read DTC and "pending" codes. Says you can view definitions for generic codes, but you can only get the code number for manufacturer specific codes.

I see after looking this stuff up, I used it wrong. I was supposed to let it scan KOEO and I just did it while it was running. So when my wife gets back from work (tomorrow AM) I think I'll scan it again. I'm not expecting to find a code though, since key on-off-on-off-on displayed "NONE" on the odometer. If there are no codes read, I wonder if it would do any good to do an erase?

Anyone happen to have a schematic on this? I could read the wheel sensors with my oscilioscope if I knew where to look. I hate to go to the dealer, not only the cost/incompetance factor, but it's a big hassle to get there while they are open.

Oh, I see a toothed ring near the front end sensors, I assume the sensor counts teeth. Do these get gunked up? Is there any point to pulling the sensors to inspect or clean them?

 

[SteelHeadz]

Thanks, Mikey.


Haynes says I need a DRB scanner tool, what ever that is. I think I'm gunna put that Haynes in the can and use it for toilet paper.

Scanner I have is a 9040 and the book says it can scan all global (generic) obd II codes.It can read DTC and "pending" codes. Says you can view definitions for generic codes, but you can only get the code number for manufacturer specific codes.

I see after looking this stuff up, I used it wrong. I was supposed to let it scan KOEO and I just did it while it was running. So when my wife gets back from work (tomorrow AM) I think I'll scan it again. I'm not expecting to find a code though, since key on-off-on-off-on displayed "NONE" on the odometer. If there are no codes read, I wonder if it would do any good to do an erase?

Anyone happen to have a schematic on this? I could read the wheel sensors with my oscilioscope if I knew where to look. I hate to go to the dealer, not only the cost/incompetance factor, but it's a big hassle to get there while they are open.

Oh, I see a toothed ring near the front end sensors, I assume the sensor counts teeth. Do these get gunked up? Is there any point to pulling the sensors to inspect or clean them?

The DRB 3 is a Chrysler Scantool that reads/scans all the modules for DTCs, Monitors and actuates sensors and is also used to Program or Flash the Modules. It also has a built in Labscope..Anyways, Schematic diagram is not a biggie, i've attached the wheel speed sensor diagram for you. if you need additional schematics, let me know what component you need it for. and , YES , the Teeth you see on the back of the wheel bearing assemblies are the TONE RINGS.. each of the wheel speed sensors are Hall effect sensors, it relies on the gaps between the toothed rings for reference of speed. if at any point in time that one of the tooth breaks or get's mangled or even an accumulation or metal particles stuck together with grease, the reference signal from that sensor is no longer true. in this case, you may encounter a premature engagement of the ABS during a turn or even in a light braking situation.. also, the Air Gap on these sensors are preset and are not adjustable, however if the sensor has been pulled from the wire or any other means and disfigured the sensor away from its proper position, this will also give you a false signal.. If i was in your shoes, i would correct the calibration of the speedometer first just to take that out of the question.i think i've said enough or too much, but let me know what info. you need that i can help you with.

 

[knudsen]

Thank you so much. Perfect explanation on all accounts. Two out of three have connectors between them and the CPU, so I should be able to get a scope on then without piercing the wires or anything. You don't happen to have the component locator that tells where the connectors are, do you?

 

[SteelHeadz]

Here's the Connector locations. All the Sensors have connectors on them, just follow the sensor wire from the sensor and you will find a connector at the end of it. Also ,here's the Controller pinout's.
CONTROLLER ANTI-LOCK BRAKE - BLACK 25 WAYCAVCIRCUITFUNCTION1B9 18RDLEFT FRONT WHEEL SPEED SENSOR (+)2B8 28RD/DBLEFT FRONT WHEEL SPEED SENSOR (-)3G7 18WT/ORVEHICLE SPEED SENSOR SIGNAL4F20 18DG/PKFUSED IGNITION SWITCH OUTPUT (RUN)5B4 18LGLEFT REAR WHEEL SPEED SENSOR (+)6B3 18LG/DBLEFT REAR WHEEL SPEED SENSOR (-)7--8Z3 12BK/ORGROUND9A20 12RD/DBFUSED B(+)10D25 18YL/VTPCI BUS11--12Z1 18BKGROUND13B43 18PK/ORG SWITCH TEST SIGNAL14B41 18YL/PKG SWITCH #1 SENSE15--16--17B42 18TN/WTG SWITCH #2 SENSE18L50 18WT/TNBRAKE LAMP SWITCH OUTPUT19B7 18WTRIGHT FRONT WHEEL SPEED SENSOR (+)20B6 18WT/DBRIGHT FRONT WHEEL SPEED SENSOR (-)21G9 18GY/BKRED BRAKE WARNING INDICATOR DRIVER22B1 18YL/DBRIGHT REAR WHEEL SPEED SENSOR (+)23B2 18YLRIGHT REAR WHEEL SPEED SENSOR (-)24Z3 12BK/ORGROUND25A10 12RD/DGFUSED B(+)

 

[knudsen]

Wow Mikey, your gold! Thanks a zillion. Just woke up. Stayed up way too late last night as you can tell by my last post time, so I'm short on time to do much today, but I'm off to recheck the code. Thanks again.

 

[knudsen]

I got no codes again doing KOEO0 test, but I went ahead and cleared the codes that didn't appear to exist. Maybe I'll get lucky. I found some interesting info on testing hall effects and thot I'd share for other's who may need to test:

Topbuzz Web Site - Testing ABS Sensors @ www.topbuzz.co.uk

Method 1. you should be able to do with just a volt (multi) meter. If you were to ignore the instructions and measure from the plug off the CPU, you would also be checking the wiring and connectors. Need someone to turn the wheel under test for you.

Method 2 and 3 requires poking at the wires, which I'm not fond of for exterior wiring. But it may need to be done. I see pick-a-part just got a 97 cherokee in, so if the sensors are the same, I might grab a couple and make a test jig from one.

Crank sensor, but works the same: The Hall-Effect Sensor

And general theory: http://www.wellsmfgcorp.com/pdf/Counterpoint3_1.pdf

 

[knudsen]

You won't believe what the problem was in the end. My wife called me at work and said the cooling fan was running after she shut it down. So I came home and pulled the connector. That night I went to troubleshoot the fan relay, if I could have actually found it, and the battery was dead. It looked like hell, so I just replaced it. All the electrical troubles went away!