Glow plug issues

jdulle

Veteran Member
Joined
Feb 4, 2017
Location
Ithaca, NY
TDI
96 B4, 97 B4
So my new to me grey 97 b4 was a little hard to start in the cold so I replaced the glow plugs. That didn't seem to help much, so I took off the harness to check the voltage. I got voltage to all 4. Then I put it back on, and it was old and falling apart and the check engine light came on for the glow plugs. So I bought a new harness and put it in. Still the light comes on after running the engine for 20 secs or so. I checked the voltage at the 2 wires, and it was 9.2 v in one and 9.6 in the other. I am guessing they should be the same? I then checked the glow plugs by voltmeter between positive battery and top of each glow plug and got the same battery voltage (12.39). So what could it be? The wires before the harness? The battery is pretty old and doesn't have full CCA so I will be replacing that soon, which I guess could be the issue.
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
Just checking that you cleared the CEL after replacing the harness?

It's normal for the voltage at the glow plugs to be a bit lower than the voltage at the battery terminals themselves... particularly in older cars... but 9V does sound a bit low (although it proves your new glow plugs are fine). Might be worth checking for corroded connections at the glow plug relay or the fuse terminal.

Failing that, hard starting is often something other than the glow plugs: low compression, timing out of adjustment.
 

jdulle

Veteran Member
Joined
Feb 4, 2017
Location
Ithaca, NY
TDI
96 B4, 97 B4
I unplugged the battery for 30 seconds. I should probably clear the code with my reader and try again.
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
Yup, unplugging the battery won't clear that code ... it has to be done with a reader.

The ECU stores them in non-volatile memory, airplane flight recorder-style, so they can be read later even if the battery dies or is disconnected.
 

jdulle

Veteran Member
Joined
Feb 4, 2017
Location
Ithaca, NY
TDI
96 B4, 97 B4
Well I cleared them with the reader and that seems to have solved the problem. Thanks so much, glad it was that simple.
 
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