Diagnosing electronics MK4 AGR /ALH 1998

jimjay

Active member
Joined
May 23, 2011
Location
Fresno
TDI
VW NB 1998 TDI AGR VE O2J
Hello, I am in need of some guidance to help with my learning curve for electronics and diagnosing. Specifically where do you find resistance and voltages for the electronics so I can determine if part a is good or bad.

Story, 1998 VW, AGR / ALH, NB

I recently finished changing out my timing belt, the job went fine, but when done checking the timing I ran the auto scan to see how the car was doing. And found the faults, see below. I started reading and found myself thinking of part changing, I paused and started thinking about why could I have these errors and engine running fine. Well it turns out that when I used the starter to rotate the engine a few times to let the belt settle in, I didn’t have the sensor(G71,G72) connected and tripped all the faults.
Even though I had the problem solved, I hope, it tickled my curiosity. I looked at my wiring diagram to see what information it had, basically just the flow of the wires, attached below. I checked the resistance but I don’t know what they are supposed to be. I went to the Bosch site and there were not any resistances or voltage values I can use to check functionality. Where do you guys find this information?


3 Faults Found:
00575 - Intake Manifold Pressure
17-10 - Control Difference - Intermittent
00519 - Intake Manifold Pressure Sensor (G71)
31-00 - Open or Short to Ground
00527 - Intake Manifold Temperature Sensor (G72)
30-00 - Open or Short to Plus
Readiness: 0 3 0 0 0



Bosch site https://www.boschautoparts.com/en/auto/pressure-sensors/low-pressure-sensors?partId=0281002177
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Well first you are overthinking this.

However, the appropriate shop manual will have some of these checks.

But normally we look at the engine data so we can see what the ECU sees, and check to see if it is within an expected range.

Intake temp for instance if the value is checked after the car has been parked and is cooled down to ambient that value should also be pretty close to whatever the ambient temp is. As far as where it should be during operation it depends on the load, the level of requested boost, and of course the charge air cooler's efficiency which obviously is better on colder days.

Boost is easy: the ECU knows what it should be, and this data is displayed as Actual vs. Requested. The ECU knows that "if the RPM is XXXX, and your right foot is at XXXX, and the volume of air into the engine as read from the MAF is XXXX, then I want YYYY level of boost, and the N75 is duty cycled accordingly.
 
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jimjay

Active member
Joined
May 23, 2011
Location
Fresno
TDI
VW NB 1998 TDI AGR VE O2J
Hello oilhammer, Thank you for your reply. The logic takes more experience i was hopping to speed up the experience learning curve with data, possibly a cheat. Which shop manuals are you talking about, I have Bentley's and I cant find that info in there.
 

STDOUBT

Veteran Member
Joined
Jul 30, 2007
Location
Portland, effing Oregon
TDI
dos jettas
From reading your codes, I bet if you examine/clean up/repair any fouled
wiring / connectors at your MAP harness and the IM temp sensor harness,
then clear your codes they might just go away.
Check, clean any grounds you can find too.
 
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