Speed signal and Odometer not working

[commvr93]

I have a Toyota Lexcen Jan/1994 which is a commodore VR V6 3800 Automatic Gear.

My problem started when the odometer was not working. So I took out the instrument cluster to have a look at it. I could not find anything wrong with it. I thought that it could be bad connections between the back of the instrument cluster and the 3 wiring square connectors where it goes into it. I cleaned all the connectors on both sides and tensioned them up a bit. That did not solve the problem. On the contrary I lost the speed signal and the tachometer. I did not disconnect the negative from the battery and I accidentally left the ignition key sitting in the lock in the totally off position. I thought maybe I damaged the cluster. So I bought a second hand one from a wrecker dealer and installed it.

The fuel,temperature and tachometer guages are working. The speed signal and the odometer are still not working.

I noticed, when I am driving, a repeating clicking sound is coming out of the Body Control Module. When I stop driving, the clicking sound stops. Is there a relation between the BCM and the instrument cluster?

I had a look at the speed sensor on the automatic gear. There was a bit of oil leaking. I sprayed it with a degreaser and cleaned both terminals. I still have the problem.

Can anyone help?

[Brett_jjj]

Hi, Id start by checking error codesChecking error codes VR/VS (Revised).It could be one of the sensors.If it doesnt show anything then you might have to see someone with a scantool that can read to/from the BCM(Body Control Module).Im not sure whether the BCM controls the speedo or not.Id have thought the speedo would be controlled by the vehicle speed sensor(VSS).Someone here will know for sure though.They might be unrelated issues.

[Brett_jjj]

I just checked out the wiring diagram in the gregorys repair manual and it shows the speed sensor going to the BCM then the speedo .(not sure if the speedo gets it signal from it though)But its a chance the clicking noise from the BCM is the cause of the speedo not working.

[88GreenVN]

Good chance it's the speed sensor that is faulty.

[commvr93]

Hi Brett,

Thank you for your great idea. I did what Darren suggested in checking the error codes. I got 12 for three times. Does this mean that the BCM is in good working condition. If it yes, then what other tests I can perform myself before thinking of replacing the speed sensor.

[commvr93]

Hi,

Thank you for your reply. If it is the speed sensor. How can I replace it myself without too many hassles.

[commvr93]

Hi Brett,

I just had a look at the gregory's service manual No. 265.

I am looking at page No. 257. It shows that the speed sensor is connected to the ECU at B6 and B5.

Page 261 shows the speedo on the instrument cluster connected to the ECU. The BCM is also connected to the instrument cluster. My BCM is "low" series. The BCM and the speedo are fused to No. 10. I do not have a trip computer in my car.

Could it be that the ECU is not reading the speedo?

There are two things to check. 1) Test the physical wiring between the speed sensor and the ECU connection at B5 and B6. 2) check the terminals on the speed sensor and test if it is OK? How do you that and what to look for when testing it?

Taking into consideration that we have already tested the computer and we got 12 for three times.

I would appreciate some guidance here. I have a multi-tester and all the necessary tools to solder or do minor electrical repairs.

[commvr93]

Hi Brett,

I meant to test speed sensor and not the speedo. My apology for this oversight

[andyman]

disconnect the battery and check continuaty in the wiring between the speedo sensor and the ecu have the multimeter set on ohms to check this, if you got the wires right the reading should be as low to 0.00 as possible, anything upto 0.40 on the positive side of a circuit and 0.20 on the negative is allowable, but lower is best

[hako]

Also wobble/push/pull the wires to the speed sensor as the wires can break inside the insulation due to heat or impact with foreign objects.

[delcowizzid]

if the ecu wasnt getting a signal it would spit codes most likely between the ecu and dash

[commvr93]

Hi,

I did what you recommended. I am getting different ohms " 0.215,0.040,0.885,0.759 and keeps on changing. I tried it again on my old analaogue multimeter and it gave me 0.040 but after several tests it changed to 0.835.

I tested the resistance on the speed sensor it is 1.320 and steady.

I physically tested the two wires going to the ECU from the speed sensor connector. they are fine. there is no sign of deterioration on the ECU side.

The BCM no more clicks. I went for a test drive after doing all these tests. The speed signal and the odometer are still not working.

How can I test if the BCM is OK. It is a body control unit . Everything else in the car works fine. Lights, fans,remote key, auto doors locking, engine start. I am just wondering where would the fault be?

I am becoming more inclined at replacing the speed sensor and see how I go with it. I can get a cheap one from an auto wrecker place. The only thing I am worried about I do not like to touch the auto transmission system. I do not want to be in one problem and then add another one.

I had a look at the sensor. There is a hexagonal head small bolt holding the sensor into the back of the automatic transmission. I am wondering if I loosen this bolt will the oil from the trans gush out? Also is it as simple taking the bad one out and immediately replacing it with the good one?

Please guide me because I need to be prepared for any eventuality especially when I am underneath the car and there is not much room to maneuvre.

[commvr93]

Hi,

If the ECU is giving the all clear code on the dash "12" does this mean that the BCM is also in good condition?

[Brett_jjj]

Did you let it go through for a while,because it flashes a code 12 three times, then flashes any errors that may be logged.If after the first 3 times,it then keeps flashing code 12 ,then its all ok.I just wanted to check with you about this.

[commvr93]

Hi Brett,

Thank you for this very important point. I did not let go through after the first three flashes of 12. I must tell you also that I tried it several times and let if flash for 3 times and switched off without running the engine.

I just went outside and did the test again and let it flash for over 10 times. I am getting code 12.

What does this mean? What is "all clear" indicates?

Does it mean that the BCM is good and nothing wrong with it?

I started another thread to change the speed sensor, but another member was telling me that because the car has an automatic transmission which is working allright and it is changing speed then the speed sensor should be good otherwise the auto trans would not work! In other words the car computer will not give the proper command to the auto trans. if it is not getting a signal from the speed sensor. This eliminates the doubt about the speed sensor. Where else to check or test the speedo system.

[Brett_jjj]

The code 12 means no error codes set.You might have to see a mechanic with a diagnostic scanner to see if there is any problems anywhere like in the BCM etc.I just dont know what else can cause this to happen.Have you checked all the fuses under the dash?

[88GreenVN]

I'd check the regulator PCB for dry solder joints (cracked) It's behind the speedo in the cluster

[commvr93]

Hi Brett,

I checked all the fuses one by one. What I did not check are the 30 Amps relay switches . The square looking black Bosch ones. There are 3 in the dash next to the blinker flasher and 6-8 in the fuse box next to the car battery. Could there be a problem in one of these?

Another test just came up to my mind. I want to test the wire coming from C5 on the ECU the Violet/White stripe going to the second connector on the dash, which goes to pin No. 2 for the speed signal on the cluster and isolate the BCM. I am going to take off the negative from the car battery and run a physical test with a Multimeter to check if the wire is OK and to check if the wire goes through the BCM or not! I'll let you know how it goes.

[commvr93]

Hi,

Where is the regulator PCB exactly. Is it inside the cluster? where the 9 pin dark brown connector goes into?

[88GreenVN]

Hi,

Where is the regulator PCB exactly. Is it inside the cluster? where the 9 pin dark brown connector goes into?

http://forums.justcommodores.com.au/...09-bit-fix.jpg

This is the PCB ^^^ it is inside the cluster (yes has a ribbon to it at the top) behind the speedo unit. You take the speedo out and you will see the PCB.

This can be a weak spot with the cluster and give grief with the gauges/tacho/speedo.

[commvr93]

Hi Brett,

Follow up on my post No. 18. I finished checking and testing the Violet/White Stripe coming out of the ECU at C5 and going to Connector 2 pin 2 for the speed signal. The wire was good. It had a good circuit, no breaks in the wire. Also I isolated the three connectors to the BCM one by one to check if it does have any effect on the connection between the ECU and conector 2 , none whatsoever. In other words the BCM is not connected to the speed signal wiring coming out of the ECU.

What else to check?

[commvr93]

Hi,

Thank you for your quick reply. I know exactly which PCB you are talking about. I will do the checking . Even I will add a bit more soldering to make sure that it is well soldered.

I will let you know how it goes.

[88GreenVN]

Hi,

Thank you for your quick reply. I know exactly which PCB you are talking about. I will do the checking . Even I will add a bit more soldering to make sure that it is well soldered.

I will let you know how it goes.

I've fixed a few now and found a sharp scribe and outside light the best way to go. Run the scribe over the solder joints looking for and thing that is not completley smooth.

and if you cant find anything with the eye or scribe - solder it up anyway

[commvr93]

Hi,

I soldered over the three points on the regulator on the PCB. Put the cluster together and drove the car. I still have the same problem. The speed signal and Odometer are dead.

I tracked with my multimeter the pin No. 2 on connector 2, which is for the speed signal and followed the line on the green sheet board it does not go to the 9 pin connector on the PCB. It goes directly to a small 5 pin connector that goes to the Speedo instrument. If you look from the top at the cluster where the 5 pin connection is , it goes to pin no. 2 on the right or pin no. 4 from the left hand side.

I am just wondering,coming to this stage of testing with a multimeter, if I can check what would be the right milivolt or miliamp coming from the ECU to the speedo. I have found the relevant wire which is the Violet/White stripe at C5 from the ECU going to the speedo no. 2 connector at pin 2. The wire is good no breaks but I could not test the voltage or the current . What would the parameters be?

Also if I want to test the speedo on its own, can I connect it to a 1.2volt AA battery or a tiny watch type button battery and check if it is working? What do you reckon?

[commvr93]

Hi All,

I have got good news. I have been scratching my head over the weekend. I went through all the threads I started and through all your replies. I also started a process of elimination and went through the sequence of events that lead to the speedometer and the odometer not working. I ended up that the problem would be between the BCM and the cluster instrument. My checking of the replaced BCM eliminated that there is something wrong in the original one. So I started testing the connections at the back of the cluster instrument and found the problem. The printed copper lines on the green coloured plastic sheet are so delicate. Any wrong movement can cut or split them easily. So I started checking all the connections on No. 2 connector going to the speedometer and there it was. I could not see it with the naked eye. I looked with a magnifier and found a very tiny split in the line going to No.11 on the No. 2 connector. Looking at the electrical drawing page 261 on the service manual from Gregory. It is the Earth. This is why the speedometer was not working.
The way I fixed it is by applying a thin strip of aluminium foil along where the cut was and fixed it with adhesive tape. It worked.

My special thanks go to Delcowizzid. I strongly recommend reading his notes and advice. He knows what he is talking about. It saved me changing the speed sensor where almost everyone asked me to replace.