I have an 1986 vette that has abs problems , ( i believe bosch 2). once it goes through self check at 4 mph, abs light comes on. I am looking for a scanner or tool to pull codes. I show in service manual gm tool # J35890 abs tester, along with j355592 pinout box? any ideas were to locate, or superceed these?

 

there are pins you can jump on the ALDL that will set off flashing lights on the DIC. I will have to check the Helm Service Manual.

 

Bogus, I appreciate you trying to help me, for like the 3rd time on this forum. You are a prime example, once i found corvette forums, that i live here!

 

will these procedure still work on my 1986? everywhere i have been reading, Bosch 2, and my year, do not have the abs module and the ecm connected, thus not being able to pull codes via ses? I hope your right, and I am wrong though ! looking forward towards help

 

Totally bogus info. There are NO codes available via the ALDL for the 86-89 C4 ABS systems. There is no connection between the two on the early C4 ABS.

Correct. The only tool that can scan the early C4 ABS is the Kent-Moore ABS tester or the use of a 10 MegOhm multimeter and the Kent-Moore pinout box. Most dealers no longer have these tools as the early C4 is not brought in for ABS problems enough to warrant the expense, so they sell them on FleaBay. That is how I got my ABS Tester and pinout box. Drawing on my own experience and from the Aug. 1998 Corvette Fever article by Gordon Killebrew there are several checks that can be done.

First : Pull each sensor and clean with WD40. The sensors are essentially powerful magnets and they will accumulate a lot of road dust and debris which affects the sensor readings. The sensors are held in each wheel knuckle by a single screw with a 10mm head. After you clean the sensors, use a little anti-seize on the sides to keep the steel sensor from welding itself to the aluminum knuckle after you put it back in. See if that helps.

Static Test #1
Using a digital volt/ohm meter (DVOM) with a 10 MegOhm resitance, disconnect and check the resistance across the 2 pins on each of the wheel sensors. They should read 900 to 1100 Ohms. They should also all be within 100 ohms of each other. If not in range, clean with WD40. If still not in range, replace the sensor. You can pull the sensor connector where it connects to the main wire for each sensor going into the main harness, or you can disconnect the 8 pin connector in the ABS compartment on the drivers side under the plastic tray. If you use the connector behind the seat you need to get the correct pair of wires for each sensor. Check the ABS wiring diagram for you year car in the manual. For my 88 the wire colors are:
LF - yellow & blue/white stripe, RF - Green/white & brown/white,
LR - red & black, RR - brown & white.

Static Test #2
Check your laterial acceleration switch, remove the right console carpet and locate the switch behind/under the AC/blower controls. It will have an orange and an orange/black wire. Test it by holding it in your hand in the same position as it was mounted in the car and measuring the resistance with an ohmmeter. It should read zero ohms.

Then turn it 90 degrees to vertical and check for an open (or infinite reading). If it fails this test, replace it. Check the junk yard for one. Nobody usually buys them there because they seldom go bad. So you should be able to get one for about $20.

Dynamic Test #1
VERY IMPORTANT: Disconnect the main harness that connects directly to the ABS Controller first.
Note: this test is essentially the same as what the Kent-Moore J35890 ABS test tool tests in the ABS controller however, we aren't testing the relays at the same time like the K-M tool does.

Set the DVOM to AC volts and go to the 8-pin connector in the ABS compartment on the drivers side under the plastic tray (unless you have or can borrow a Kent-Moore J35592 Pinout Box). Again, for my 88 the wire colors are:
LF - yellow & blue/white stripe, RF - Green/white & brown/white,
LR - red & black, RR - brown & white.

You will need someone to make AC voltage readings for each wheel sensor while you drive at 15 MPH. The left front should read .65 millivolts and the right front close to the same. The rear sensors should each read 1.1 millivolts. If your reading is high it means the air gap at the toothed gear is too small. A lower reading would mean too much of a gap. If the air gap does not match left to right it could be caused by worn wheel bearings. If the air gap is out of spec it will cause the ABS light to come on. The air gap is not really adjustable. To decrease the gap you may need to sand the area where the sensor attaches to the wheel knuckle.

To increase the gap you need to put a layer of paper between the sensor and the knuckle. A meer fraction of an inch makes for a major change so DON'T do this unless you are sure it is not due to a loose or bad wheel bearing.

I have found that the front wheel bearings have a minor amount of play in the way that they mount to the car. Once they are bolted in, they are in solid, but they can be mounted a tiny bit more forward or aft of center. Since the toothed wheel that induces the voltage to the ABS front sensors are on the front wheel bearings, this will allow you to make a minor adjustment in voltage if your reading is slightly too high or too low compared to the other front sensor, by adjusting the wheel bearing. This doesn't work for the rear. A bad wheel bearing can cause the voltage to be off enough to set the ABS light. That was the cause in my case.

Dynamic #2
Take you car to a dealer or someone who has a Kent-Moore J35890 ABS Tester. It will perform a dynamic test of the entire system, including the relays. I bought a used one for $150 on eBay. They sold new for $500. Make sure that if you take it to a dealer, that they have the correct and working ABS tester for the early C4. The Kent-Moore tester is the GM Authorized tool. If the dealer suspects that it is the ABS Controller be sure to get in writing, that if replacing the controller doesn't fix the problem, you don't pay for it. They are over $900.00 new from GM. If the controller really is faulty, you can get a replacement from a junkyard for about $300 or maybe less. I know that there were some at my local Corvette junkyard for that price.


Another point of failure is one of the 3 ABS relays. According to my GM Parts & Illustartion Guide the 1986-1989
C4 ABS system all use the same 3 relays. The GM Part #s are:
1636973 .... RELAY, ELEK CONT
14105967 ... RELAY, PRESS MOD VLV SOLENOID
14105968 ... RELAY, PRESS MOD VLV PUMP MTR => Replaced with GM part # 12513302

The 14105968 relay was replaced with a GM unit of different internal design. It is the first relay I would replace and then follow that with a new 1636973 unit. Superior Chevy 800-728-8267 can get all 3 for you at a major discount to the usual GM dealer price.

If you do all of the above except Dynamic #2 and still cannot resolve the problem, drive your Vette to CA and I will test your controller for you with my Kent-Moore ABS test unit. Good luck.

Mike

 

Nice post, Mike

 

If its failing right at the self test speed (pump check) it is likely the pump motor relay, related connections or possibly a bad pump motor.

Remove and reinsert all the the relays, maybe tap the motor case with a hammer to unlodge potentially stuck brushes. Try this again as the motor is activated, if you can. Maybe difficult to do while driving. Get a trunk monkey to help.

Does it improve if you cycle the igntion off then back on when rolling at greater vehicle speeds (above the normal pump check velocity) maybe 20 mph or so?

If it is an auto trans car you can bump the starter into the crank position while in gear briefly to cycle the ignition without shutting the car off. The neutral saftey switch should prevent the starter from cranking, but the ignition and ABS will be reset. Stick car shouldn't crank unless the clutch is all the way in so this should also work.

If it improves at higher speeds after the ign is cycled, this points to a low output wheel speed sensor due to improper airgap, bad sensor or poor connections.

Also if you get it to initialize (turn the lamp off) after an ignition reset at speed, force some extended abs events on a gravel road to give the unit an opportunity to cycle the pump and valves for a few seconds.

 

Mike and Tequilaboy: nice post and good info...

 

will work on today after b-day party! thanks for all the good info here. i appreciate all the help!