Silverado Monitors Set and Then Clear/Reset - Please Help!
Good evening Everyone. I have this 2007 Silverado I am diagnosing Due to the monitors getting ready and all of a sudden clearing on their own. Customer stated monitors were clear after shutting vehicle off and restarting. I drove the Vehicle to verify the customer concern.
What I noticed was while driving it will also clear the monitors no drivability concern whatsoever. So my next step I monitored the hot at all times voltage at the ecm. I noticed no drop outs, So according to me my next step would be installing a new ECM since all the voltage and grounds checked out OK. No aftermarket devices installed on this vehicle that I could find.
Customer decided to go with a used ECM I programmed it install it drove it and same thing. I would turn over at times shut off the ignition turned it back on after a minute the monitors were clear. Sometimes will driving the monitors will be ready and just clear. Anybody ever experienced this problem or can guide me in the correct direction what am missing? Thanks in advance .
Grounds? What is the voltage drop on kam or battery direct to pcm during cranking and running, also voltage drop at the pcm on the ground circuit cranking and running. Odd that clears as you drive , ac voltage ripple perhaps? I'd like that if we post ,(yes the voltage is good) , we put some numbers up .ie I checked circuit 1234 and the voltage drop was .1 v during cranking and ..49 when running. That way we can put something tangible to problem at hand.
You say it doesn't have any drivability issue , so I doubt something is shorting reseting the pcm.
Are you trying to pass IM test ? I would assume you are .You may have to get it ready and go hope for the best.
We inspected them all and cleaned them up . . Just lost in this . Don’t know what way to go next
Did you monitor "keep alive" power at the pcm when shutting off and then restarting the engine? A weak battery can allow the voltage to dip far enough to clear the memory yet still start the car.
I did monitor the voltage with a scope . Also with my min n max function and nothing . I tested the battery and it passed . I also tested it while monitoring voltage and it dropped to 8v while cranking .
I don’t think so I’m thinking it’s ok at 8v . the Scope min max picks up 7.94 at its lowest but I can see my voltage line drop to like 9 v
Seems too low to me... anything below 9.5v or 10v I think is too low
It all depends on how you test the battery. I don't trust those digital/computerized testers.
It is too low! but why would it reset running? He is essentially load testing the battery with the starter, It would be nice to know the starter current with the battery that's in there and with a booster on. A trick I use is if you have a carbon pile is to load it to the cranking voltage , read your amps< when you hit that voltage there's your starter current .Although we need to make sure our battery is of good health ie 12.6 open circuit before you begin. Amp clamp is really the way to go, but some battery cables are not easy to lasso. Not all this and it's a bad battery , nah no way , ,
I will try lomad testing with my current clamp . And the battery test on my pico only other option I have .
How long was it at 8v? If it was just a couple milliseconds on initial crank then it's probably ok. I'm not sure what the threshold is but if it stays that low long enough (maybe a couple tenths of a second) that will reset your keep alive memory.
I have seen many cars with a good battery drop to around 8.5v on initial crank when the starter current is at it's highest. This drop only lasts a few milliseconds.
8v is lower than I typically see with a good battery.
I was just re-reading your post as I write this and I noticed you said it cleared the monitors while driving the car? Are you saying that some monitors were "ready" and then while driving you saw the monitors go to "not ready" on the scan tool?
Yes exactly that . After replacing the ecm . I test drove it , got the 02 sensor ready in like 6 mins . I pulled over shut off the vehicle and restart and did it one more time and still ready I was thinking good it’s fixed . I drove it and i was looking at my monitors and I saw the 02ready and just go to not ready . I used diff scan tools as well
Wow, I have never seen or heard of that, that's crazy. I didn't even think that was possible. As far as I know, monitors can only be returned to "not ready" by a code clear or power cycle.
If I didn't know you already replaced the PCM that's what I would suggest. At the moment I don't know what else to tell you.
im lost too . Customer said he had a fpcm installed recently . Since the last emissions test . It’s a dorman
8v is too low do yourself a favor and rule out the battery by installing a fresh one. Not sure about the loss of monitors while driving. the way you put it I wonder if the scan tool took time to refresh the screen after a stop and restart. Also check starter current while voltage drops on crank may be drawing too much bring voltage low.
That’s what I was also thinking maybe . But it took atleast 4 mins after I had turned it off and started driving . I will install a new battery
How about pin tension? Wiggle testing while monitoring with a scope? Engine torque/movement?
I checkled pin tension at pcm and all good . I did find dielectric grease from a previous person being there
I have hade some weird things with GM in general, but one time in particular I hade a similar situation and it was the ignition switch, it will loose the voltage while driving.
Check your ignition that may be your issue.
I will keep checking and Also check the power modes in the bcm
Had A Chrysler one time that would reset all monitors when spiked by an ignition coil. But that had the coil primary controlled directly by the PCM, unlike the GM style coils.
I think I'd wanna watch the "Run Time" while driving to see if it resets when the monitors clear. That would confirm a PCM "reset"
I'd also watch current misfire counter to see if there's a miss that you aren't feeling. If you do see one cylinder with a hick-up, I'd be suspicious of a secondary to primary voltage spike that's causing the PCM to reset.
Rusty, I think your on the right track with the computer getting spiked. Nothing else makes much sense since this happens while driving.
I have had vehicles with a bad battery wipe out the monitors on start up. Make sure battery voltage stays up. Also check for corrosion or any other source of a voltage drop in the starter system.
Sorry for the repeat. The other messages did not come right up.
Following along for now. I agree with the others. Replace the battery. 8v is too low. (although I doubt that would reset monitors while the vehicle is running, still, when diagnosing a problem,you have to address known problems first,in this case a bad batery. Source voltage is one of thee most important parts of a modern, computerized electrical system.....)
2007 is this old or new body style? you stated you tested power/ground at PCM and they are OK. I would recommend a voltage drop test if not already done. I would also voltage drop your positive and negative battery cables while cranking and post your results, assuming you have a properly functioning battery. If this is a new body style, check your 2 main power feeds off the positive cable. Starter and under hood fuse block that runs through a firewall mounted mega fuse. Other than that, the only thing that comes to mind is a PCM reset from from a surge/spike. There are other things to check but lets start with these.
I have seen this. The last one was a 2004 Avalanche that I think got jump started backwards based on the facial expression of the owner when I asked.:)
Here are 2 screen captures of data when I am diagnosing one of these or something similar like a no communication issue or all readiness flags set to incomplete etc.
The first one is a bad battery, not causing flags to set to not ready but had a communication issue on restart.
The second one is the vehicle that set flags to not ready on key cycle. It also has the cranking battery voltage PID but doesn't drop as low. Pay attention to non-volatile memory PID and LTFT PID. Those tell me the PCM is losing voltage to non- volatile memory which are pins 20 and 57 C1 or the PCM is damaged. The latter was the case.
Basically, set your scan tool to these PIDs and see what it tells you.
So after speaking to the customer I found a bit of info . This car passed emissions two years ago no problems . After this the only repairs made were a new fuel pump control module . This new fpcm is a dorman product . I have my doubts ,but could this be causing the monitors some how to clear.? He said they didn’t program it . It was just plug And play , it came Programmed already. . What I would do next is reprogram it and drive it ..
I spoke to the Product Manager over electronics at the AAPEX show last week. He told me that they load their electronics with a base calibration. So in many instances the calibration does not match the product. Dorman is now promoting the RAP module so that each module can be programmed with the factory calibration. If you have a Tech2, you can read the calibrations in the vehicle and then go on to the TIS website and check against what the truck should have. tis2web.service.gm.com/tis2web Since you have covered the easy stuff, it is great that you are thinking outside the box.
So I tried to flash the module. The dorman one, and I got this message. All my connections were ok so I tried again. Same results turned off pc and same results. So I’m thinking something Is wrong here, why doesn’t it let me flash it? It would at least pull up and tell me the calibration is the same etc, right? Or maybe this module isn’t supported I’m thinking? But why? It’s on the list.
I had already checked powers and grounds at the pcm and all ok never dropped out while driving, pin tension ok as well. I thought it was the pcm. Also No aftermarket devices like alarm etc, But no not the PCM.
At this time Im already eating the pcm, luckily he went with the used Module so I’m not loosing much, just hair. So with the dorman module in the picture now I tell myself I can scope the data lines right and try to prove something with the waveform but mind you, this truck has no other driveabilty symproms, no codes, nothing. So would I be able to interpret the data lines and the bytes and see that it’s clearing codes? Maybe maybe not. So I never scoped the data lines :(
Since I have time into this and I’m lost. And as much as I like to research, I also need to make money, right? My technician hat comes off and my service advisor hat goes on. I explain to the customer my findings, and as an educated guess which way to go next. So he approves an oem used fuel pump module. I get the module install it, open tis web and I am able to program this module I just get the I am attempting to flash with the same calibration window come up.
So I go against GMs recommendations and flash it anyway. Start the truck have the customer drive it and so far It’s good the key has cycled many times and the truck has been driven all afternoon today. So far only two monitors left, EVAP and HO2S...
Wow! That's great news so far! If this actually fixed the issue, it's good to get this thing out the door. I'm sure you're tired of seeing! Lol BUT you did learn off of it too. So you lost hair, eh? Just a few 😉
Actually and luckily I didn’t loose hair lol it just turned grey lol ..
I used to work for Dorman. It would benefit us all if you call in and see if you can speak to the product manager. The product manager for electronics is Demetrious. It is pronounced demeetoree. He is very interested in what is going on with Dorman electronics. He will want you to send in the part. Make sure that Dorman works with the local supplier to get a labor claim submitted.
I will call the customer i gave him the old part as he is going to return it back to autozone .try to I’m guessing . I’ll ask him to give me details on it , as to what store he is going to return it in at . Thank you
Where can I find the number To call? . I am getting the module back but the customer wants to get refunded . You think that would be posssible if I send it in?
The number I have is … I am sure they have a way to refund the part. I can't speak for the process as it may have changed in 5 years. They are in the Philadelphia area so their hours are on Eastern time. M to F.