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Tach stopped working

B

blueanchorgtp

New member
Suddenly my tach stopped working. Had car apart, put in new radiator, ported blower, replaced radio, front door speakers, and new pcm then started it and no rpms. Switched tachs to a spare and still nothing. Rpms work from obd2. What should I start checking? Replaced speed sensor on tranny already. Mph works and so does HUD.

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the fact the car starts and runs means you're getting the 13x and 24x signals from the crank to the ICM and the PCM.
the fact that you are able to see RPM over the OBD-II connection means the PCM can see and output the signal.
the fact you swapped dash modules and it doesn't work on either means the tach signal isn't getting to the IP cluster.
the fact that MPH works says that the MPH signal is getting to the cluster

both RPM and MPH are driven by the same data as the HUD and OBD-II. I can't find a good reference online for the cluster wiring, but I will check my service manual tonight and post back again later.
 
Take a look at the connector on the ICM. I bet you bumped it when you did the radiator and maybe hosed the wire..IIRC white?
 
Probably not what's going on, but I had this happen when my abs module went out. Do you have an abs warning light?
 


mguzzo said:
the fact the car starts and runs means you're getting the 13x and 24x signals from the crank to the ICM and the PCM.
the fact that you are able to see RPM over the OBD-II connection means the PCM can see and output the signal.
the fact you swapped dash modules and it doesn't work on either means the tach signal isn't getting to the IP cluster.
the fact that MPH works says that the MPH signal is getting to the cluster

both RPM and MPH are driven by the same data as the HUD and OBD-II. I can't find a good reference online for the cluster wiring, but I will check my service manual tonight and post back again later.
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Ok thank you

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blueanchorgtp said:
Car always had abs light, prior to problem as well

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Might be worth looking into. I know the tach runs through the abs and if the module is removed the tach doesn't work, not sure about if it isn't working though. But I have to agree with bill, I'd think if this was the case, you'd have both mph and tach issues.

If you have someone who can scan abs codes though, might be helpful, if not not for this, for the abs issue! Lol
 
Haha well, they definitely are related! Just pulled up the schematics, and the ip tach and abs tach are both ran from the pcm. I'm betting you get a abs code for no tach signal. Below is the schematic. You'll want to start by testing pin 8 of C2 (clear connector). You remove the air box to get to your pcm, 7mm bolt to remove the connectors (I'd remove to check for corrosion and replace for testing) . A few plastic clips on the back and zip ties you remove the grey protector and under that the pins are literally labeled. I think it will read 1-6v AC (not dc) and you'll want to do a continuity test to the ip pin P on C2. Either there's a break in the wire, an issue with the pcm, or corrosion on the connector. Good luck!
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wstefan20 said:
Haha well, they definitely are related! Just pulled up the schematics, and the ip tach and abs tach are both ran from the pcm. I'm betting you get a abs code for no tach signal. Below is the schematic. You'll want to start by testing pin 8 of C2 (clear connector). You remove the air box to get to your pcm, 7mm bolt to remove the connectors (I'd remove to check for corrosion and replace for testing) . A few plastic clips on the back and zip ties you remove the grey protector and under that the pins are literally labeled. I think it will read 1-6v AC (not dc) and you'll want to do a continuity test to the ip pin P on C2. Either there's a break in the wire, an issue with the pcm, or corrosion on the connector. Good luck!
20180306_092028.jpg
20180306_090955.jpg

20180306_090001.jpg
Click to expand...
Car had the abs wiring harnesses missing when i bought the car, never had this issue until now and I've had the car for months

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blueanchorgtp said:
Car had the abs wiring harnesses missing when i bought the car, never had this issue until now and I've had the car for months

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No offense, but there's an issue now.... the tach should work fine without the ebcm as I stated in the post above, what you need to figure out

1. Whether the pcm is actually sending the tach signal at all (test by probing the pin on the pcm)

2. If the pcm is sending the signal, where the break is. It's that simple.

Once you verify that the pcm is indeed sending the signal, it might be easiest to just run another wire to bypass. I would start though by checking where they cut the abs wire if that's what they did. It could be shorting out or grounding. Hope that clears up my above post!
 


wstefan20 said:
No offense, but there's an issue now.... the tach should work fine without the ebcm as I stated in the post above, what you need to figure out

1. Whether the pcm is actually sending the tach signal at all (test by probing the pin on the pcm)

2. If the pcm is sending the signal, where the break is. It's that simple.

Once you verify that the pcm is indeed sending the signal, it might be easiest to just run another wire to bypass. I would start though by checking where they cut the abs wire if that's what they did. It could be shorting out or grounding. Hope that clears up my above post!
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The harness is just taken off, there's extensions from the engine bay to the main harness

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blueanchorgtp said:
If I get the rpms from the obd2, wouldn't that mean I'm getting the signal from the pcm?

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Yes, you're getting signal from the pcm, but not the same one. The pcm sends this data over class2 data to the obd2 port. The instrument panel gets it from the pcm with its own dedicated line as stated above. Therefore, you can have obd2 data fine but not to the cluster. All this means is that the sensor signal is reaching the pcm.

Again, it's probably going to be easiest to just re-run that wire after you verify it's sending signal at all at the pcm with the multimeter.

I wish there was an easier way, but the options are to either run a new line or figure out where the old one is broken.
 


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