SpinningDorito

iTrader: (2)

That ground point in the center should be the radio. At least on my radio's wiring, it was separate from the main harness. Not sure if that was the previous owners handy work, or Mazdas though.

Regarding the gauge cluster hood, if I were to do it again I'd replace the springs with some good neodymium magnets. I'll definitely be making that switch next time I have mine out.

I can only think of two ground points near the rats nest. One goes from the chassis on your firewall to the engine block near the UIM.

The other attaches beneath the rats nest directly to the engine block. I can't imagine any way you could see it well with the rats nest in based on how it was attached in my vehicle. It was between the rats nest bracket and one of the bolts that holds that bracket on.

bake3310

Yesterday I was checking the gauge cluster with my DMM (digital multimeter). It seems like I have good continuity between ground (a point on the metal of the dash crash bar) and C1-01 1E as well as the ground screw of the tachometer. I also checked that I have +12VDC on the correct screw of the tachometer.

What I found that was unexpected was that I had +9VDC on the signal screw of the tachometer (key in the on position, tach showing ~750rpm, engine not running).

I suppose better info would be to have an oscilliscope on the screw, but I don't have one of those at home right now.

Any thoughts on this?

bake3310

So, I drove the car today, yes all back together with the required extra stuff that always seem to happen when you take something apart. I got on it just a bit and the CEL came on.
well, I suppose it is time to take a look at that.
6 blinks.
looks up code.
no vehicle speed sensor input.
so, I suppose I have an answer to that.
i am going to have to pull it out, give it a check, and possible replace.

Gen2n3

iTrader: (1)

Dave,

My apologies for the delayed reply. Given your recent work and observations, you could first verify the wiring between the vehicle speed sensor and instrument cluster. Unplug the Vehicle Speed Sensor (VSS) connector then unplug the C1-01 3-Series connector.

You can use the chassis ground to help measure the resistance of this length of wire. Pick one end that you will use to take measurements. On the opposite end, short the suspect wire to chassis ground using a jumper wire. Then take your measurement, which should be a short (under 2 ohms). If you see a flashing or steady "O/L" or "1. " that means the wire is open (infinite resistance). Be sure to check for cross-wire shorts between the 2 wires.

For example, measure from Connetor C1-01 3-Series. First measure the resistance from Pin 3A of C1-01 to C1-08 (Orange wire lead). Place a jumper wire on C1-08 Orange lead to chassis ground (make sure it's bare metal). Now take the resistance measurement. Place the red lead on Pin 3A and the black lead to chassis ground. It should read 0 Ohms (or close to it). This is a good indication.

Next, check for a cross-wire short. Move the red lead of your DMM to Pin 3C of C1-01 and keep the jumper wire on C1-08. Take a measurement and it should read "O/L" or "1. " which is an open. Remember, this is a good indication because you just verified that the wires from Pin 3A to C1-08 Orange lead are not shorted to Pin 3C.

Then repeat this process for the Pin 3C wires. Make sure you move the jumper wire during this step to C1-08 Green lead.

Do both wires check good? If any wire reads open then the problem rests in your car's wire harness and further troubleshooting is needed. If a cross-resistance check indicates a short then that too is a problem in the car's wire harness. Otherwise, once the Vehicle Speed Sensor is disconnected from the wire harness then you could still test it while in the car - just connect the DMM to each lead of the VSS then have an assistant rotate the wheels. If you don't see a voltage as mentioned in the BEM then, Bob's your uncle! A new VSS would be in order.

bake3310

Hi George,

Okay, so I unplugged the VSS at the transmission so I could get to the two wires in the harness going to the cluster.

I had a friend put a jumper between 3A and 3C. With my Fluke I checked continuity between the pins at the sensor. That checked out okay.

So I'm sure that the wires from the harness to the gauge are okay.

I tried to take the VSS off, but that little 10mm head bolt that holds it on is being pretty stubborn and if I tried anymore it would become rounded off. If I want to get it out, I'll have to get that brace and exhaust out of the way.

Gen2n3

iTrader: (1)

Dave,

Did you check for resistance between Pin 3A and Pin 3C without the jumper? Additionally, did you check each pin separately - Pin 3A to ground and it tested good? Then did you check Pin 3C to ground and it checked good? If you only installed a jumper between these 2 wires and measured a short then that would not provide a full picture.

I helped out another forum member using this diagram to help paint the picture of using chassis ground to help read wires. It was here: Electrical Problems Post 25. There is an additional figure in Post 38 that uses a modified section of Diagram B1a from the WDM. Advise in that thread was at a basic level so it should be easy to follow without being condescending or trying to offend anyone's intelligence.

Were you able to test the VSS while the connector was removed? I'm sorry to hear that its removal is a real PITA. Have you coated the bolt with some penetrating oil? You may need to let it soak for a day or two before trying to remove it again. Do you have a breaker bar that you could exert added leverage?

bake3310

I did not do the separate check. In my electrical engineering experience I have not found a difference between a continuity test and a resistance test.

But, since I do have it apart right now, I'll do the additional test.

I did test the VSS with the connector removed, but I should do it again with a helper as I was trying to hold the a pins with my USB oscilloscope to the pins while also spinning the wheel.

As always, thanks for the help.

Gen2n3

iTrader: (1)

Dave,

Cool! Looking forward to reading about your results.

bake3310

So I did the resistance checks also. I connected the wires at the socket of the VSS to ground (one at a time) and measured the resistance at pins 3A and 3C. Both measured about 4ohms (which is also about the measured resistance of my jumper wire). I also checked for cross shorts which came up negative.

So I then attempted to remove the VSS again. New day, new result. I was able to move the bolt and with a little leverage out it came...and about a liter of tranny fluid. Which I was surprised by, but should not have been.

With it out I was able to reliably spin the little gear and have my meter's probes on the contacts. Sure enough, no change in voltage.

Have any recommendations on where I can get a new VSS? Doing a quick search on the part number I found this:
https://www.oemautopartz.com/mazda/o...nsor-bv6517400

Gen2n3

iTrader: (1)

Dave,

Good to hear that your wires from the VSS to instrument cluster all check good. Not to mention that you positively identified a bad VSS. As for getting the replacement part, give a shout to Ray Crowe! He works for Mazda and can get OEM parts sent to you for a decent cost. He is also an FD owner and he knows the parts fiche inside, out, backwards, and upside down! His info can be found here: Ray Crowe is back in action-Post 106

I'm sorry to hear that the VSS held back the gear oil. How much of a mess did it make? The good news is that you diagnosed and found the problem with your speedo!

Redrocketjoe

Kudos to all the smart electronics folks out there chasing down electrons on their own. I however will have to have a pro do the work due to gross incompetence. Mind if I ask for good results lately on cluster refurb, particularly the dead odometer?

DaleClark

iTrader: (55)

Michael Gagne on Facebook is a wizard at cluster repair. He did mine and does excellent work, he knows these clusters backwards and forwards and has a custom calibration and test machine to verify they are working 100%.

Dale

Redrocketjoe

Thanks Dale, I am contacting by MG by FB Message. Be nice to have a working odo again! Does the ECU remember actual mileage and will correctly reflect actual since odo display died? Asking for a ignorant friend

GasGasJDM

Does anyone has the contact of this guy Michael Gagné? I'm also in troubles with two different clusters. In one, no ODO, RPM or SPEED (RPM and SPEED went to zero simultaneusly while driving). The other one is one I just received from Japan and everything works, but RPMs show like 1.5 times the real value, and speed changes linked to RPMs.

Anyone has an idea on what can be the the issue for these clusters? For the first one I'm suspecting either a power issue (no power arriving to both RPM and SPEED dials), or the chip that is receiving sinusoidal signal and transforming them into squares.

For the second ones seems like RPM signal is being filtered somehow to speed.

zli944

iTrader: (2)

Not familiar with Michael but Geoff fixed my cluster (zensation on the forums here). He's actively promoting an OLED odometer for the cluster as well which looks very look.

Apparently not. Geoff let me know it's usually the power supply circuit that often fails for the odometer, in which case the processor is not receiving power and thus not converting speed into tracked miles.