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Temp gauge dead, but vagcom picks up coolant temp

erasedhammer

Active member
Joined
Sep 2, 2019
Location
Maryland
TDI
1996 Passat
1996 Passat TDI.

Temperature gauge in gauge cluster always shows nothing, seems completely dead.
Hooked up my vagcom scanner and it can read the coolant temperature just fine.

Does this mean that the gauge is the problem and not the actual sensor?
 

Nuje

Veteran Member
Joined
Feb 11, 2005
Location
Island near Vancouver
TDI
2015 Sportwagen; Golf GLS 2003; 2016 A3 e-tron
I don't know about the Passat, but there are four pins on the Mk4 G/J/B cars. I don't know the pin-out, but I'd guess that one goes to the gauge, one to the computer, one for ground and one for...good luck(?).

Who knows. But I've seen something similar on one of my G/J/B cars, and sure enough, replacing the coolant temp sensor made everything work properly again.

Again - I may be way off base, but that's my $.02. Open to correction.
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
Northern MD (HAGERBUSH)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress)
not uncommon for the cluster to have issues, i would not be surprised if the wiring harness behind the dash is damaged or that the PCB has started to delaminate the solder points. easy way to find out, pull the cluster out, its very easy to do, test the wires coming into it for the cluster and inspect the cluster and or test it, not sure what the volts and ohms range is supposed to be for the coolant gauge but im sure someone else can chime in.
I would just get a scangaugeII and put it some place easy to see without taking your eyes to far from the view ahead. the temp gauge was and is fairly uselss as it has a wide range that just shoes strait up normal temp reading. you can start to overheat the engine and the gauge will still say its ok. worthless POS vw garbage.
 

erasedhammer

Active member
Joined
Sep 2, 2019
Location
Maryland
TDI
1996 Passat
not uncommon for the cluster to have issues, i would not be surprised if the wiring harness behind the dash is damaged or that the PCB has started to delaminate the solder points. easy way to find out, pull the cluster out, its very easy to do, test the wires coming into it for the cluster and inspect the cluster and or test it, not sure what the volts and ohms range is supposed to be for the coolant gauge but im sure someone else can chime in.
I would just get a scangaugeII and put it some place easy to see without taking your eyes to far from the view ahead. the temp gauge was and is fairly uselss as it has a wide range that just shoes strait up normal temp reading. you can start to overheat the engine and the gauge will still say its ok. worthless POS vw garbage.
Yeah I wouldn't mind it, only the coolant light is flashing at me. I figured they are connected problems... maybe just low coolant.
 

JETaah

Vendor , w/Business number
Joined
Jan 18, 2001
Location
mi 48836
TDI
96 B4V, 1999.5 jettaIV,2005 BEW Beetle
Yeah I wouldn't mind it, only the coolant light is flashing at me. I figured they are connected problems... maybe just low coolant.

Could be that the reservoir's probes for the coolant level are coated with funk and giving a false reading if your coolant level appears to be right. On A4 cars they are exposed where you can run a brush across them to clean them. Don't think that they are accessible on the Passat's reservoir.
If that is the case then a replacement reservoir is not that expensive.
https://www.idparts.com/coolant-expansion-tank-a3b4-p-1157.html
But do a continuity check on the harness leads to the ECU or cluster...don't remember if they go straight to the cluster or not.
Do you have any signs of contamination (bathtub ring) in the reservoir?
 
Last edited:

erasedhammer

Active member
Joined
Sep 2, 2019
Location
Maryland
TDI
1996 Passat
Could be that the reservoir's probes for the coolant level are coated with funk and giving a false reading if your coolant level appears to be right. On A4 cars they are exposed where you can run a brush across them to clean them. Don't think that they are accessible on the Passat's reservoir.
If that is the case then a replacement reservoir is not that expensive.
https://www.idparts.com/coolant-expansion-tank-a3b4-p-1157.html
But do a continuity check on the harness leads to the ECU or cluster...don't remember if they go straight to the cluster or not.
Do you have any signs of contamination (bathtub ring) in the reservoir?
I think it's just dirty on the outside.
I'll check it today, but I don't recall seeing any fluid in there....
Engine still stays at temperature, IR temp monitoring, so I never bothered to check the coolant level
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
1996 Passat TDI.
Temperature gauge in gauge cluster always shows nothing, seems completely dead.
Hooked up my vagcom scanner and it can read the coolant temperature just fine.
Does this mean that the gauge is the problem and not the actual sensor?

The scan tool data comes from the Engine controller side of the CTS, not the gauge side. And on that car, the Instruments work a little differently than the newer cars.

The sensor for the older cars used to be 357-919-501-A but got superceded to 6U0-919-501-B some time in the last decade. I would try that first, cheap and easy.
 

AndyBees

Top Post Dawg
Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Temp sensor is the problem .. follow Oilhammer's advice.

The same issue is going on with my 03 TDI Jetta, the gauge is on zero. I plan to change it when I do the TB job. I've seen this numerous times.
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
Northern MD (HAGERBUSH)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress)
The scan tool data comes from the Engine controller side of the CTS, not the gauge side. And on that car, the Instruments work a little differently than the newer cars.
The sensor for the older cars used to be 357-919-501-A but got superceded to 6U0-919-501-B some time in the last decade. I would try that first, cheap and easy.
so why then does my 98 jetta have a 0 reading on the scangauge when i disconnected the temp sensor on the upper hose? i thought the b4 and the jetta both had nearly the same engine?
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
That is not the sensor we are discussing. That is for the A/C and A/C alone. Has zero to do with the Engine controller, or the gauge in the Instruments.
 
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