B4 Passat TDI exhaust sensors (?) question

tdi_in_va

Member
Joined
Jul 19, 2016
Location
Virginia
TDI
B4 Passat
Hello TDI Club, I have a question about the exhaust of B4 Passat TDI. Please see the diagram I found in this post:

http://forums.tdiclub.com/showpost.php?p=1705407&postcount=7

Items number 5 and 6 in this diagram are an "L" shaped metal probe or sensor of some kind, that screw into a threaded port in the exhaust. There is one at the cat inlet, and one at the cat outlet. So it must be for measuring exhaust temperature? Or oxygen sensor? I don't know. I don't see any visible part numbers, and the two probes look identical.

Either way, I have two B4 cars. One has these sensors properly screwed into the exhaust, and the other has these two sensors coiled up and zip-tied under the car dangling loose, not attached to the exhaust. On the second car with the loose sensors, the exhaust does not even have the two ports to screw them into!

Can someone explain what the function of these are, and why one car would have them hanging loose with no where to screw them into?

FYI I do have a Ross Tech VCDS, which shows no error codes on either car, and both cars run great.

Thank you
 

ketchupshirt88

Veteran Member
Joined
Oct 31, 2012
Location
waupaca, WI
TDI
2005 Passat daily, a bunch of others in the graveyard out back...
Are both 1996 b4's???

if so, id guess its for the 5th injector stuff. i don't think it is monitored by ecu but hopefully someone more knowledgeable on that system will chime in.
 

tdi_in_va

Member
Joined
Jul 19, 2016
Location
Virginia
TDI
B4 Passat
Yes, both are model year 1996. I can try to get a photo of them, in case that parts diagram isn't clear.
 

Abacus

That helpful B4 guy
Joined
Nov 10, 2007
Location
Relocated from Maine to Dewey, AZ
TDI
Only the B4V left
The '96 had them and they are temp probes related to the 5th injector, which only worked on the automatic B4's, none of which made it to a North America. You can read the outputs in the VCDS but it's not meaningful since it's too far down the pipe.

The '96 without them probably had the exhaust replaced at one time.
 

tdi_in_va

Member
Joined
Jul 19, 2016
Location
Virginia
TDI
B4 Passat
The '96 had them and they are temp probes related to the 5th injector, which only worked on the automatic B4's, none of which made it to a North America. You can read the outputs in the VCDS but it's not meaningful since it's too far down the pipe.

The '96 without them probably had the exhaust replaced at one time.
Very interesting, thanks!
 

Camel413

Veteran Member
Joined
Jun 22, 2010
Location
South East Missouri
TDI
96 Passat Wagen Totaled, 95 Passat GLX future conversion
Ok just a quick question about this. I have a 96 B4 with manual with these sensors in the cat. What is up with this 5th injector, I have not heard of this before. I am going to the exhaust shop next week to get a straight pipe installed. I havent decided if I want to remove the cat or not yet. If I do are these sensors basically worthless? If I remove the cat can I just cut the wires and still be ok? No engine lights or problems?
 

ToddA1

Top Post Dawg
Joined
Aug 3, 2011
Location
NJ 08002
TDI
'96 B4V, '97 B4 (sold), '97 Jetta (scrapped)
If cut off and the ECU is running stock programming, you'll likely get a CEL. This is why the OP said his were tied up. IIRC, some people have removed them with no CEL. YMMV.

You can cut them out and add resistors to get rid of the CEL.

-Todd
 

Jaceb-GTF

Member
Joined
Sep 30, 2016
Location
Sturgis, MI
TDI
96 B4, 91 ECOd
Was also curious about this! My 96 has the GQ replacement ECU instead of the BK, so i was thinking that ECU doesnt even register that the 5th injector and temp probes are there.
 

RIP TDI

Top Post Dawg
Joined
Feb 16, 2000
Location
Santa Barbara, CA
TDI
'15 GSW SE 6MT...... '01 Golf GLS 5MT.... '96 Passat Variant....
No, the GQ still looks for temperature values of the sensors even though injector solenoid is inactive.
 

Lug_Nut

TDIClub Enthusiast, Pre-Forum Veteran Member
Joined
Jun 20, 1998
Location
Sterling, Massachusetts. USA
TDI
idi: 1988 Bolens DGT1700H, the other oil burner: 1967 Saab Sonett II two stroke
The sensors can be left electrically connected and tied up out of the way.

Down stream sensor is hot indicates the cat is hot and no added 5th injector fuel is needed.
Upstream sensor is cold means there's not enough heat to ignite fuel from the 5th injector, so no 5th injector fuel is added.
Upstream is hot and downstream is cold and the 5th injector adds fuel to more quickly get the cat up to efficient operating temp.

Or so it was intended.

In reality the 5th injector with BK ECU was almost always running with a hot or cold cat, manual or auto.
The GQ did not activate the 5th injector but still monitors the sensors and will throw a fault code for implausible readings (open circuit, or short to ground, or great differences between the two).
 

jhax

Veteran Member
Joined
Jan 24, 2012
Location
Golden, CO
TDI
96 Passat B4V, ALH engine out of a 2002 Jetta, some IE Rods and ASV Pistons. Nothing drivable yet though
Does anyone know what size resistors to be used between which pins to remove CEL?
 
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