HELP! Oil pressure light is blinking for no reason???? and Tach question.

Lemon

Member
Joined
Oct 17, 2010
Location
Golden BC
TDI
1996 Jetta
I have a 96 Jetta Diesel. Th oil pressure indicator light has blinked as long as I have owned the car. The mechanics have checked it out and the pressure is fine. I'm trying to sell the car and want to get the light to stop. I was hoping it was just going to be one of the oil pressure switches, changed them both out and the stinking thing still blinks away????
Any advice/ideas on what to check out next?....

Also the previous owner disconnected the tachometer and I can't figure out how to reconnect it?

Please get me pointed in the right direction.

Thanks!
 

Joe_Meehan

Top Post Dawg
Joined
Sep 3, 2005
Location
Ohio USA
TDI
NB TDI, 2002.5, Silver
I would guess you need to find a VW mechanic with the proper diagnostic tools. Check out the list of recommended mechanics here.
 

ewenmaclean

Veteran Member
Joined
Jul 19, 2010
Location
Edinburgh UK
TDI
T25 with 1.9 AHU
Hello,


from what you say I wonder if the two things are related to the wiring to the dash. A blinking oil light could be an earth leak on the low rpm low pressure oil sender - if it were the high rpm one it would only blink if disconnected about 2000 rpm. The blue/black wire from the low oil joins to be a red/white wire joining a 28 pin connector at the dash on pin 9. The tacho signal from the ECU is a green wire which joins the same connector at pin 10. I'd check the wiring out at this connector.

Hopefully it's not the dash pod itself that's wrong. I have a different dash I'm afraid so couldn't help you there. Hope you get it sorted

Ewen
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
On your car both the tach and the oil pressure warning system take their RPM cues from the W terminal on the alternator.

So, your two problems have something very much in common.

Perhaps the PO didn't so much "disconnect" the tach as not repair an issue with the alternator or the wiring to the cluster.

With an AC voltmeter you should see 8-10VAC at the W terminal with the engine running.

Here's a picture of the pinout of the back of the alternator:




If you've got signal there you can check the wiring at the back of the cluster to see if it's making it there:



Pin 10.

If all this is good you've likely got a defective cluster... very common on MK3s these days, and unfortunately finding a diesel MK3 clusters with a tach is getting tricky. I have a diesel cluster with a clock if it comes to that for ya.
 
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ewenmaclean

Veteran Member
Joined
Jul 19, 2010
Location
Edinburgh UK
TDI
T25 with 1.9 AHU
Hello Vince Waldon,

good advice - sorry if I mistakenly said the ECU sent the tacho signal - it does on my ECU and I thought it'd be the same. Can I just ask how you know which it is for a 96 Jetta - your wiring diagram is a bit different from mine for the AHU.

Ewen
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
No worries.

In Canada a 1996 diesel Jetta will very likely have the AAZ IDI engine with the fully mechanical injection pump... so no crank sensor or ECU. We didn't get TDI engines on Jettas for a couple years after they were introduced in Europe.
 
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