When I replaced the Lower Intake Manifold gasket on my 98 blazer I created a wiring problem. Aftre the repair I have the following problems.

EVAP Fuel Tank Pressure sensor reads high 7+v.
Fuel gauge is always full
PO1631 and B2960 codes are set and the security light is always on.

The Passlock failure started as a no run condition and after multiple relearns I ended up in this condition.

I must have stressed some wiring under the hodd, but I'm not sure where all these circuits intersect. Under the hood because that is where I was working.

Probably a serial data problem since the fuel level is reported properly (scan tool can read it).

Anybody know what circuits and what wires run where?

Thanks
Kevin

 

i know on the older vehicles if the gauge would read way past full it meant you had a ground issue. make sure there wasnt any wires that were supposed to be screwed back in with a bolt somewhere for a ground. i remember doing that years ago at work and took a while to find it

 

Since I was working on the LIM and that caused the problem I am focusing under the hood. No grounds were removed to work on the LIM, but I'll check out that possibility. I found a wiring diagram that shows that there is a VCM output for fuel level.

VCM C1 BLUE PIN 9 Fuel Level Output PPL ckt 30

What I don't know is if the data is serial data, voltage or resistance to the IP. I'm not even confident that this output is used by the IP. I'm still looking fr a description of how the IP fuel gauge gets the information from the VCm or BCM.

Kevin

 

I should also mention that the PCm is reporting both a PO452 and a PO453. Sorry, I was just reporting the BCM codes earlier.

 

You are making this way more complicated than needed...
When you were in there, you pinched (grounded) or broke (opened) a wire (circuit) somewhere. It wasn't that way before so find and correct it. Then reset your ECM and see what happens.

 

So I am working my way through the fuel gauge/sender circuit and using the thread https://blazerforum.com/forum/tech-a...agnosis-43922/ and my alldatadiy.com subscription.

Problem is nothing tells me where the 6-pin connector is located. Can someone help?

@bandidolenny Thanks for that advice. If I knew where the problem was I'd fix it directly. Lots of wires and trying to find the right ones.

 

okay. The fuel gauge is now working. Wish I knew why, must have moved the right wire while looking for, and not finding the problem.

Cleared codes and still have the P0452 being set. Moving the connector to the fuel pressure sensor at the tank causes the values to move around. Will need to drop the tank a bit to work on that problem. The fuel pressure is in inHg not volts. 7.34 is low according to the ECM

Interestingly enough wiggling the wires at the top of the fuel sender, I think this is the fuel pressure sensor wire, put the vehicle back into Passlock security fuel shutout - going through the 30 minute relearn procedure now. The Fuel pressure reading would move all over the place when wiggling those wires.The relearn completes and runs, but keeps going back to the fuel cutoff mode. Must share a common ground or reference voltage.

Does anyone know where the other end of this circuit ends. I believe I need the location for the 6-pin connector identified above. That will let me isolate the short location.

 

Did you possibly leave a ground strap off somewhere? Make sure that you have a good ground from the engine to the battery, as well as from the body to the battery.
Almost sounds like an ECM issue... I wonder if you may need to reflash the computer?

 

Wow. I've been having some of the same problems. The security light has been a constant thing for a few years now. I've bypassed the passlock system and put in my own resistor. But every so often it acts up and I have to put the BCM back into learn mode again.
Then last week the CEL popped on, scanned it and it's the EVAP code, so I got a new EVAP Solenoid but haven't gotten a chance to put it on.
Then yesterday I was cruising down the freeway and it magically made gas. And eventually just pegged out full and has been stuck there since.
I'm thinking that the BCM itself is bad based off the the Passlock issue (it's not remembering what resistance should be there). And wondering if maybe the gas gauge is due to the BCM as well?

1998 Blazer LT