ABS problem

[frehol]

Blazer 95 4WD 4WAL
The ASB lamp ligths up at startup, goes off for about a sec and then on again. Had the ODB-II scanned and there where no error codes stored, but the mecanic said that it looked like the ABS thought the wheels were running at 3 km/h (= 2mph) but veichle speed was read 0 km/h. The veichle was parked with no wheels turning at the scan moment.

Have checked the front wheels speed sensors and they look all right after I cleand off some dirt and metall dust...

Rear wheel speed is given by VSS, but so is the veichle speed parameter too, so how can I have two different speeds (rear wheels and veichle speed) given by the same sensor?

How to fix the problem?

/Freddy

[ricksza]

Originally Posted by frehol

Blazer 95 4WD 4WAL
The ASB lamp ligths up at startup, goes off for about a sec and then on again. Had the ODB-II scanned and there where no error codes stored, but the mecanic said that it looked like the ABS thought the wheels were running at 3 km/h (= 2mph) but veichle speed was read 0 km/h. The veichle was parked with no wheels turning at the scan moment.

Have checked the front wheels speed sensors and they look all right after I cleand off some dirt and metall dust...

Rear wheel speed is given by VSS, but so is the veichle speed parameter too, so how can I have two different speeds (rear wheels and veichle speed) given by the same sensor?

How to fix the problem?

/Freddy

That's the default reading of the module. It won't display any lower reading.

[Southern Comfort]

DIAGNOSIS & TESTING
NOTE: When testing and diagnosing 4WAL system, use of Tech 2 scan
tool is required.
The Electronic Brake Control Module (EBCM) performs a selfdiagnosis
of the ABS system. The EBCM detects and isolated system
failures, then sets the corresponding diagnostic trouble code (DTC).
Before diagnosing 4WAL system, perform a comprehensive visual
inspection of system by checking wiring harness connectors, harness
routing (pay particular attention to wheel speed sensor wiring harness
routing), applicable fuses in fuse block, and ground connections.
Ensure brake fluid level in master cylinder reservoir is full.
Start 4WAL system diagnosis using DIAGNOSTIC SYSTEM CHECK. If
failures are found when performing diagnostic system check, you will
be directed to enter diagnostics to retrieve DTCs or perform SYMPTOM
TESTS. Diagnostic system check may indicate that system is functioning
properly.
C0221 .................. Right Front Wheel Speed Sensor Circuit Open
C0222 ................ Right Front Wheel Speed Sensor Signal Missing
C0223 ................ Right Front Wheel Speed Sensor Signal Erratic
C0225 ................... Left Front Wheel Speed Sensor Circuit Open
C0226 ................. Left Front Wheel Speed Sensor Signal Missing
C0227 ................. Left Front Wheel Speed Sensor Signal Erratic
C0229 ................................ Simultaneous Dropout Of Front
C0235 .................................... Wheel Speed Sensor Signal
C0236 ........................ Rear Speed Sensor Signal Circuit Open
C0237 ............................. Rear Speed Sensor Signal Missing
C0238 ............................. Rear Speed Sensor Signal Erratic
C0241-C0254 ................................... Wheel Speed Mismatch
C0265 or C0266 .......................... EBCM Control Valve Circuit
C0267 or C0268 ..................... Pump Motor Circuit Open/Shorted
C0269 or C0274 ....................... Excessive Dump/Isolation Time
C0271-C0273 .................................... EBCM Internal Fault
C0281 ......................................... Brake Switch Circuit
C0286 ....................... ABS Indicator Light Circuit Shorted To
Battery Voltage
C0288 ....................... Brake Warning Light Circuit Shorted To
Battery Voltage EBCM Relay Circuit
(1) - Always perform DIAGNOSTIC SYSTEM CHECK before performing DTC
tests.
DIAGNOSTIC SYSTEM CHECK
NOTE: For circuit reference, see WIRING DIAGRAMS.
System Description
The diagnostic system check is an organized approach to
identifying a problem created by an ABS malfunction. It must be the
starting point of any ABS complaint diagnosis because it directs to
the next logical step in diagnosing the complaint.
Serial data is exchanged by EBCM through harness connector
C1, terminal "F", and Class 2 data is exchanged through harness
connector C1, terminal "G". EBCM is supplied switched ignition voltage
through harness connector C1, terminal "A", and ground is provided
through harness connector C1, terminal "J".
Diagnosis
1) Verify all EBCM connectors are connected properly. Install
scan tool. Turn ignition switch to RUN position. Using scan tool, try
to communicate with the EBCM. If data is being received from EBCM, go
to next step. If data is not received from EBCM, go to step 4).
2) Using the scan tool, record any current or history DTCs.
If any DTCs are present, see 4WAL DIAGNOSTIC TROUBLE CODE (DTC) table.
If DTC(s) are not present, go to next step.
3) Turn ignition off for 10 seconds. Turn ignition switch to
RUN position and observe the ABS indicator lamp. If the lamp is on for
3 seconds then goes out, the system is operating normally. If not, go
to step 11).
4) Turn ignition off. Disconnect the 10-way EBCM harness
connector. Turn ignition switch to RUN position. Measure voltagebetween EBCM harness connector terminal A and ground. If the voltage
is between 10-15 volts, go to next step. If not, go to step 9).
5) Disconnect negative battery terminal. Disconnect 10-pin
EBCM harness connector. Check resistance between negative battery
terminal and 10-pin EBCM harness connector terminal "J". If resistance
is 0-2 ohms, go to step 6). If resistance is not 0-2 ohms, go to step
12).
6) Inspect EBCM and EBCM harness connector terminals for poor
contact. Inspect battery terminals and battery cable terminals for
poor connection. Repair as necessary. Is there a poor connection, then
go to step 7). If connections or terminals are okay, go to step 8).
7) Repair the poor connection. After repairs, go to step 1).
8) Reconnect EBCM harness connectors and battery terminals.
If communications cannot be established between scan tool and EBCM,
try scan tool on similar vehicle with the same system to determine if
scan too is malfunctioning or if Class 2 data line is faulty. See
appropriate diagram in DATA LINK CONNECTORS article in WIRING
DIAGRAMS. Repair or replace as necessary.
9) Disconnect positive battery cable. Turn ignition switch to
RUN position. Measure resistance between the positive battery cable
and terminal A of the EBCM. If the resistance is 0-2 ohms, go to next
step. If not, go to step 13).
10) Turn ignition off. Remove 10 amp ABS/Brake fuse. Measure
resistance between EBCM terminal "A" and ground. If the resistance is
infinite, go to step 15). If not, go to step 14).
11) Observe the ABS light. If ABS light stays on, go to step
18). If not, go to step 21).
12) Repair open or high resistance in circuit No. 451. After
repairs, repeat step 1).
13) Repair open or high resistance in circuit No. 441. Check
10 amp ABS/Brake fuse. After repairs, repeat step 1).
14) Repair short to ground in circuit No. 441. Check circuit
breaker. After repairs, repeat step 1).
15) Inspect ignition and brake switch input circuits and 10-
pin EBCM harness connector C1 for physical damage, which could cause a
short to ground with EBCM harness connector connected to EBCM. Repair
as necessary. If damage is found, go to step 16). If no damage is
found, go to step 17).
16) Repair damaged terminals. After repairs, go to step 1).
17) Check 10-amp ABS/Brake fuse. If the fuse is good, replace
the EBCM. After repairs, repeat step 1).
18) Use scan tool to turn off the ABS light. If the light
goes off, go to next step. If not, go to step 20).
19) Replace the instrument cluster. After repairs, repeat
step 1).
20) Replace EBCM. After repairs, repeat step 1).
I hope this helps. I do have the schematics for the abs as well.

Circuit Description
The EBCM controls the ANTI-LOCK indicator light by supplying
ground to turn on or battery voltage to turn off the indicator light.
If indicator light is off constantly, check for an open or
short to voltage in the light circuit between indicator light and
EBCM. Also check for open in GAUGES fuse or faulty light bulb.

Diagnosis
1) Perform Diagnostic System Check. If diagnostic system
check has been performed, go to next step. If not, go to DIAGNOSTIC
SYSTEM CHECK.
2) Turn ignition off. Disconnect 10-pin EBCM harness
connector. Using a fused jumper wire, jumper terminal "B" of 10-pin
harness connector to ground. Turn ignition switch to RUN position. If
ANTI-LOCK indicator light illuminates, go to next step. If not, go to
step 4).
3) Inspect 10-pin EBCM harness connector for damage or
corrosion. If connector is okay, go to step 9). If connector is not
okay, go to step 8).
4) Inspect jumper wire fuse. If fuse is blown, go to step
10). If fuse is okay, go to next step.
5) Inspect 10-amp GAUGE fuse. If fuse is blown, go to next
step. If fuse is okay, go to step 7).
6) Turn ignition off. Replace fuse. Turn ignition switch to
RUN position. Remove and inspect GAUGE fuse. If fuse is blown, go to
step 13). If fuse is okay, go to step 14).
7) Remove and inspect ANTI-LOCK indicator light bulb. If bulb
is okay, go to step 12). If bulb is faulty, go to step 11).
8) Repair 10-pin EBCM harness connector.
9) Replace EBCM.
10) Repair short to voltage in ANTI-LOCK indicator light
circuit between EBCM and instrument cluster.
11) Replace ANTI-LOCK indicator light bulb.
12) Repair open in circuit between fuse block and instrument
cluster, or ANTI-LOCK indicator light control circuit between
instrument cluster and EBCM.
13) Repair short to ground in brake warning light control
circuit between instrument cluster and EBCM.
14) Problem is an intermittent short to ground in brake
warning light control circuit between instrument cluster and EBCM.Thanks
SC

[frehol]

Thanks SC, it was a very complete answer to my question!


//Freddy

[frehol]

OK, I found that the front right WSS don't work as it should. When rotating the wheel the sensor gives a 300mV output but the resistance is infinitiv.
Have ordered a new hub with WSS ( >2000SEK = aprox. $250).
Whith some luck there is no more problem...

I am a bit annoyed that my mecanic didnt find it with his scan tool :-(

I probably get the new hub to the weekend so I can change it then..
//Freddy

[mike2004tct]

Originally Posted by frehol

I am a bit annoyed that my mecanic didnt find it with his scan tool :-(

//Freddy

I might be wrong, but doesn't the ABS system require it's own scan tool, not the ODBII port?

[blazes9395]

Nope, the same port is used, you just need the right scanner, or a capable scanner. The ABS system is controlled by the same computer that controls engine management/operation.

[blazes9395]

Originally Posted by frehol

OK, I found that the front right WSS don't work as it should. When rotating the wheel the sensor gives a 300mV output but the resistance is infinitiv.
Have ordered a new hub with WSS ( >2000SEK = aprox. $250).
Whith some luck there is no more problem...

I am a bit annoyed that my mecanic didnt find it with his scan tool :-(

I probably get the new hub to the weekend so I can change it then..
//Freddy

I am surprised your mechanic didn't find or figure this one out. If you have a reading that is higher (or in this case a wheel showing a different speed than the rest), you should start looking at each wheel sensor. This is where the computer gets its information from. It could still work, but be giving the wrong value, and the ABS system cannot figure out whats happening. The scanner gave him the answer, it was right in front of him.

And the '95 does not have the sensor integrated into the hub, like the newer models do, its separate. The sensor is on the wheel dust cover. The hub only has the wheel sensor ring, not the sensor itself. If the wheel hub is alright, you don't need it then.

[frehol]

Originally Posted by blazes9395

I am surprised your mechanic didn't find or figure this one out. If you have a reading that is higher (or in this case a wheel showing a different speed than the rest), you should start looking at each wheel sensor. This is where the computer gets its information from. It could still work, but be giving the wrong value, and the ABS system cannot figure out whats happening. The scanner gave him the answer, it was right in front of him.

Well, he claimed he had tha right scanner and that there where no codes stored and that tha ABS looked fine in the scanner... I don't think he took it for a test drive Will not use him again...

Originally Posted by blazes9395

And the '95 does not have the sensor integrated into the hub, like the newer models do, its separate. The sensor is on the wheel dust cover. The hub only has the wheel sensor ring, not the sensor itself. If the wheel hub is alright, you don't need it then.

My parts dealer said it is intergrated. He got the VIN year of the blazer and I thought he should know what part I needed. Will see when I take it apart...

//Freddy

[frehol]

Originally Posted by blazes9395

And the '95 does not have the sensor integrated into the hub, like the newer models do, its separate. The sensor is on the wheel dust cover. The hub only has the wheel sensor ring, not the sensor itself. If the wheel hub is alright, you don't need it then.

Looks like you where rigth, blazes9395.
Just recieved the new hub WITHOUT ABS sensor even thou it said on the box it should be one...
Someone is going to get a not so happy call tomorow!
I specificely asked for a ABS sensor (WSS) and got told I had to change the whole hub becuase the WSS was integrated with the hub!

//Freddy