2007 Express 3500 Passlock voltage not pulling down

Mike Technician Georgia Posted   Latest   Edited  
Updated
Driveability
2007 Chevrolet Express 3500 6.0L (U) 4-spd (4L60-E)
B2961
B3031

This one is a crank and no start. It was at another one of our locations and they had it towed to us. It cranks and stalls immediately. When I got it, I went out to try and it started. It actually ran for quite a while. However the security light stayed on. I did a scan and found B2948, B2958, B2961 and B3031 in the BCM. I documented the codes, cleared them and let it sit for a while and worked on something else. When I came back to it, it would crank but stall immediately, as did for the other shop. I then scanned again and got B2961.

PIDs: Engine->Acc/Theft->VTD Fuel Disable switches to ACTIVE when cranking. BCM->Data->Security Passlock voltage remains at 5v when cranking. BCM->Data->Inputs: the pids for ignition switch position all change corresponding to key position. so switch is working. However the PID Key In Ignition always reads NO no matter what.

The security light does not stay on.

The other shop replaced the Passlock sensor (part of ignition switch housing), lock cylinder and key, and the body control module. All dealer parts. The repair lasted less than 2 weeks.

At the 3 wire harness for the Passlock sensor, I have 12v on the orange/white wire and good ground on the tan wire. I have good continuity on all 3 to the BCM. The yellow wire is the Passlock sensor wire. It has 5v and the sensor pulls that voltage down when the key is turned. It is a Hall effect sensor and the magnet is in the lock cylinder. No chip in the key.

We're a fleet shop and it's an Express, so there's usually always a couple of others in our parking lot. There was a "known good" one that matched perfectly. I brought it in, probed C3A6 on it and watched the voltage drop from 5v to I think 2​.​something when I turned the key. Perfect! Everything works. I swapped the lock cylinder from our dead problem van into the known good and it fired up, same drop on C3A6. Put the lock cylinder from good into our dead one and turned the key, no drop. I didn't move the bad van's Passlock sensor over though. A little more involved to do that and good van had to go home soon.

At the BCM, I probed the yellow wire, pin A6 on C3. The voltage always remains at 5v. (4.95 to be exact) So our first thought was "oh well the other shop got a bad Passlock sensor." So we replaced the brand new Passlock sensor. Same thing. 5v at C3A6 at every key position. I unplugged the Passlock sensor. C3A6 remained at 5v. If I'm reading correctly, the Passlock sensor gets 12v in and at key off returns 5v to the sensor signal, pulling that 5v down at key on. Is that correct? EDIT: Did some more reading and confirmed I read correctly. The Passlock sensor gets 12v from the BCM (orange/white wire) and produces the 5v on the sensor signal (yellow) wire.

What am I missing? There's just not that many parts to this. Passlock sensor, 3 wires, and a Body Control Module. No chip in the key. The Hall effect Passlock sensor works off magnets in the lock cylinder which was also replaced and worked fine in another van when tested.

0
Todd Mobile Technician
Alberta
Todd Default
 

Ground the 5 volts at the passlock hall sensor and read what the voltage is on the scan tool.

+1
Default Ð Awarded
Mike Technician
Georgia
Mike Default
   

I'll go in a little early in the morning to try that. Should I ground it to ground or to sensor ground (tan wire)? Edit, I should say 'sensor return'

0
Default Ð Awarded
Todd Mobile Technician
Alberta
Todd Default
 

Yes. I aassumed you had checked the sensor ground but check using signal return. If it shows 0V then you know the ground is good and that means those 2 circuits are good. If it doesnt go low, try grounding it to bat. neg. Should go to 0V.

0
Default Ð Awarded
Matt Educator
Ohio
Matt Default
 

Just a thought but I used to have similar problems chasing intermittent security codes on the pickup trucks. I can't remember if they are exactly the same but try tilting the steering column all of the way up, then down to see if the problem shows up. I found terminal tension problems at the base of the column at connector C201. When you tilt the column it pulls on the harness.

0
Default Ð Awarded
Mike Technician
Georgia
Mike Default
 

Matt, this isn't a tilt wheel and not intermittent.

+1
Default Ð Awarded
Matt Educator
Ohio
Matt Default
 

OK I guess it rules that out, just some thoughts.

0
Default Ð Awarded
Caleb Diagnostician
Indiana
Caleb Default
 

So for some reason new AC Delco Passlock sensors do not drop voltage anymore. Dont ask me why because I dont know. Here is my question. If you put in the new sensor/housing etc. and plug everything in. Regardless of the security light being on or off, does the learn timer count up on the scan tool and start over after 600 seconds?? If so, lets see if you can do a 30 min learn an get this thing…

0
Default Ð Awarded
Mike Technician
Georgia
Mike Default
 

It does not. And this is a 2007 so not exactly new. My Verus is 19.2. No timer for VTD learn, just active/inactive and it stays on inactive. I did try the learn anyway and it was a no go. When you say new, do you mean all the replacements or just from a certain year on up? And the vehicle did start and run long enough to pull in the shop after being towed in and then sat there idling for a while.

0
Default Ð Awarded
Felix Diagnostician
Florida
Felix Default
   

did you reprogram the pcm to relearn the security password , maybe that help, I read somewhere that when the lock cilinder or bcm is replace on a pass lock application the system must be programmed to recognize the passlock data and network password, you can configured with capable scan tool , and do the relearn with the 10 minutes 3 times until the MIL turns off

0
Default Ð Awarded
Mike Technician
Georgia
Mike Default
 

Felix, that was done and when I got it I started it and drove it in the shop. See my original post.

0
Default Ð Awarded
Todd Mobile Technician
Alberta
Todd Default
 

So, they read high but you can still learn them? Wild.

0
Default Ð Awarded
Felix Technician
Florida
Felix Default
 

To be honest not sure about that , but it seems to me that after reading your post that the hall effect sensor could be bad , kind of weird because you allready change two , or wiring problems, because as you said you should be able to see voltage drop at the bcm data list when you turn the key, hope everything turns well to you .

0
Default Ð Awarded
Caleb Diagnostician
Indiana
Caleb Default
 

Check out Joes Auto Electric on Youtube. youtu​.​be/GdfOGAlj888. There is the link. I too had an 03 Yukon same thing. 5 v just stayed there no matter the key position. But it learned fine.

0
Default Ð Awarded
Mike Technician
Georgia
Mike Default
 

This one would not learn at all. I just used a couple of backprobes and put a 2a fuse in between passlock sensor signal and passlock sensor signal return. Voltage pid dropped to zero and I got it go into learn mode and after the 30 minute procedure it starts and runs. Now it does have a P1631 set now but that's because the voltage is too low. But it does start and run.

0
Default Ð Awarded
Scott Owner
California
Scott Default
 

Mike, That would seem to suggest that one of the circuits are oversized at the Passlock sensor connector, or the magnet is not correctly placed on the lock cylinder based on what was previously done. As far as testing terminal tension I took an old sensor and broke it apart to get at the terminals. I took the board out and cut 2 of the legs off the sensor.

0
Default Ð Awarded
Mike Technician
Georgia
Mike Default
 

Except there's 5v at that sensor signal pin at the BCM with the passlock sensor disconnected. The 5v comes from the passlock sensor. Also, I tried a different lock cylinder from a running van.

0
Default Ð Awarded
Scott Owner
California
Scott Default
 

Hi Mike, "The 5v comes from the passlock sensor" Are you sure about that? The 5 volts on 1836 is from the BCM.

0
Default Ð Awarded
Mike Technician
Georgia
Mike Default
 

Yes. Passlock has 12v in from the BCM on pin 3. 5v back out to BCM on pin 1

0
Default Ð Awarded
Scott Owner
California
Scott Default
 

Hi Mike, If you disconnect the Passlock sensor what voltage is on terminal 1?

0
Default Ð Awarded
Mike Technician
Georgia
Mike Default
 

5v on 1 and 12v on 3.

0
Default Ð Awarded
Scott Owner
California
Scott Default
 

Hi Mike, So, where is the 5 volts coming from? Another so...With key rotation we're still seeing 5 volts, (on scan data at the BCM) but bringing circuit 1836 to ground circuit 1835, with a fused jumper results in scan data showing 0 volts. Wait a second that's not what you wrote above, (I think) but that's what I would have done. See B2958 steps 3 and 4. If at this point the circuit drops…

0
Default Ð Awarded
Mike Technician
Georgia
Mike Default
 

That's the thing. Very little in AllData so I read everything I could find, Identifix and elsewhere. Everything I read (and I am probably wrong) says that there's 12v in to the passlock sensor and IT produces the 5v back to the BCM and then when the key is turned on, that brings the voltage down based on the resistor in the sensor. I think the article in Identifix says something like 10…

0
Default Ð Awarded
Scott Owner
California
Scott Default
 

Hi Mike, There's very little in Alldata because GM SI doesn't have it either. All three wires to the sensor come from the BCM and that includes the 5 volt signal. That 5 volt signal from the BCM is dropped through the Tamper Resistor at the Passlock sensor. Another thing to look at would be why when looking at VTD data in the BCM, why there's 5 volts seen with the connector off the Passlock…

0
Default Ð Awarded
Mike Technician
Georgia
Mike Default
 

I was careful when probing, only went in from the back. And I do appreciate everyone's help even though I got some bad info and stuck stubbornly to it. As it turns out, there was some aftermarket stuff installed deep out of sight that was screwing with everything.

0
Default Ð Awarded
JJ Technician
Massachusetts
JJ Default
 

Is there anything on 1 with both the Passlock sensor and BCM disconnected?

0
Default Ð Awarded
Todd Mobile Technician
Alberta
Todd Default
 

Mike, this thing has 3 circuits at the hall. All terminate at the BCM. One is ground which is an internal groundin the BCM, otherwise known as signal return. Second is 5 volts coming OUT of the BCM which is pulled low to a specific voltage ranging from around from .8 to 4.5 or so. Third is a power supply to power up the sensor. This us either battery voltage but is usually lower. You did…

0
Default Ð Awarded
Todd Mobile Technician
Alberta
Todd Default
 

The P1631 is probably set because you pulled your jumper out of the Passlock connector while it was running

0
Default Ð Awarded
Mike Technician
Georgia
Mike Default
 

Todd, that's the thing. Everything I have read says that the sensor has 12v in and IT produces the 5v back to the BCM, which it then pulls low when the key is turned. At 0 v it did relearn and then start and run, but it does set a code because the voltage is below the minimum the BCM wants to see which is .75v

0
Default Ð Awarded
Raul Owner/Technician
Florida
Raul Default
 

Make sure key isn't aftermarket, how many keys are available to test? I've had sooo many aftermarket keys fail.

0
Default Ð Awarded
Scott Owner
California
Scott Default
 

Hi Raul, No special keys needed for this vehicles theft system.

0
Default Ð Awarded
Mike Technician
Georgia
Mike Default
 

Raul, no chip in the key. The key, lock cylinder, and all came from the dealer. Also, it started and drove into my bay and idled for quite a while.

0
Default Ð Awarded
Scott Owner
California
Scott Default
 

Hi Mike, Any ECM DTC's? At least with the Tech 2 the VTD is displayed in Engine Data 1. What is displayed for PCM/VCM in VTD Fail Enable, VTD Auto Learn Timer, VTD Fuel Disable, and VTD Fuel Disable Until Ign. Off? B2961 Key in Ignition Circuit - not related to the theft system. Who programmed the BCM and are the calibration files correct? Have you checked terminal tension at the Passlock…

0
Default Ð Awarded
Mike Technician
Georgia
Mike Default
 

Terminal tension is all good Scott. VTD Fuel Disable reads ACTIVE when trying to start the van. No ECM DTCs. ECM in VTD FAIL ENABLE: No, VTD Auto Learn Timer: Inactive. VTD Fuel Disable until ignition off: Inactive. Programming done in house.

0
Default Ð Awarded
Caleb Diagnostician
Indiana
Caleb Default
   

Hey Mike not sure if you saw the video in the link I posted as a reply to Todd. At this point I believe the problem lies in the BCM. I would load test all the powers an grounds to the BCM. If ok replace it with one from the dealer and lets start there. youtu​.​be/GdfOGAlj888

0
Default Ð Awarded
Caleb Diagnostician
Indiana
Caleb Default
 

I understand your dilemma here Mike. So not sure where you have ended up with this. Since you can get it too learn by grounding it why not do this. Wire in a resistor that pulls the voltage down to an acceptable range on the 5v signal circuit and then perform the learn and see if you can fix it that way, My only concern is that the signal will always stay low even with the key off. Dont know if…

0
Default Ð Awarded
Todd Mobile Technician
Alberta
Todd Default
 

There is more to this circuit than just the Passlock voltage, at least in theory. Mossman's treatise on Passlock should be required reading for everyone. Anyway, Mike never did what I said and reported is findings, instead believing that the Passlock sensor produces the reference voltage AND pulls it down.

0
Default Ð Awarded
Mike Technician
Georgia
Mike Default
 

Todd I did jumper the sensor signal to sensor return. PID for passlock voltage dropped to zero. I did go on some bad information and probably argued about it more than I should have. I do appreciate all of the help I got and as it turns out, there was more to the vehicle as I found out today. Will post that in an update to this thread.

0
Default Ð Awarded
Mike Technician
Georgia
Mike Update
 

All, thank all of you for the help. I did have some bad info and was a little insistent on it so I apologize for that and appreciate y'all being patient. We got some outside assist on the van after I jumpered sensor signal to sensor return and got it to run. Turns out there was some aftermarket wiring and relay installed that even the company that owned the van didn't know about.

+1
Update Ð Awarded
Resolution
Todd Mobile Technician
Alberta
Todd Default
 

Mike, sorry if I didn't see it in one of your replies. I just wanted you to ground the 5 volts to the sensor ground and see if it went low (0 volts) on the scan tool. Please avail yourself to Lance's Passlock article, it's out there somewhere.

0
Default Ð Awarded
Todd Mobile Technician
Alberta
Todd Default
 

I wouldn't expect this thing to learn at zero or 5 volts. I haven't watched much of the video you put up yet Caleb.

0
Default Ð Awarded
Scott Owner
California
Scott Default
 

Hi Todd, I remember that one. Something about a choice of tools to use testing the Passlock system. Educational, as well as highly entertaining. Lance was/is one creative dude, and a mechanics mechanic. Remember Auntie Lock? There was more than one time my wife caught me laughing out loud to one of his posts - "What is so funny on that auto site?"

0
Default Ð Awarded
Todd Mobile Technician
Alberta
Todd Default
 

You bet. His stuff was fantastic, funny, enlightening and most importantly, it told you how systems worked and more importantly how they failed.

0
Default Ð Awarded
Todd Mobile Technician
Alberta
Todd Default
 

There were so many great contributors. But, we are moving forward!

0
Default Ð Awarded
Anthony Technical Support Specialist
Pennsylvania
Anthony Default
 

Yup Todd, it won't be long until he is identified by the name of "Former Member". Thinking about him (or many others) in the same category as Mani sticks in my craw. Guido

0
Default Ð Awarded