CAN Bus or something else? - TerrainForum.net: GMC Terrain Forum
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post #1 of 10 (permalink) Old 10-27-2019, 01:19 AM Thread Starter
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CAN Bus or something else?

Hello all, I have a 2006 LT w/142K on it & ran into something that has me stumped. It started with a bad front wheel speed sensor which caused the abs light etc to illuminate on the dash. I disconnected the ABS 10A fuse until the new sensor came in & once installed, all ABS related lights were cleared & haven't returned. The car was due for inspection and after many miles of driving the EGR & EVAP monitors just won't pass, they still read "incomplete". I also had a stored U0073 code at this time which I did not have prior. After days of driving the code would eventually illuminate the MIL & usually go away shortly after. I've researched & tried many times to complete a 'drive cycle', but I'm guessing it's wasted effort with this code lingering around.

Since the code is communication related, I did some test at the DLC with a breakout box & DVOM. I get 60ohms across pins 6 & 14 w/good battery voltage & ground. With the system sleeping, nothing on, doors closed etc., I get 1.1v on pins 6 & 14. With the key in the on position (engine off) I get ZERO volts on pin 6 but 2.1v on pin 14. What little I know about Controller Area Networks was acquired in the past week, but from what I understand, I should be getting around 2.5v on pin 6 w/the key in the on position? Is there something going on with my CAN Hi (pin 6)? I only checked the 5v reference at the EGR & it was present!

The car still runs well other than being hard to start sometimes, only when the engine is hot. Any ideas, please share.
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post #2 of 10 (permalink) Old 10-27-2019, 07:54 AM
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I would seriously doubt you have a problem with the CAN bus itself. I’d start with the “what changed” question. You put a new wheel speed sensor in. Is it an AC-Delco sensor? Maybe it’s causing comms problems on the network? I wonder if you go back to the previous state ... does the CAN code go away?

I’ve also seen mention in the Helm Shop Manual of an admission of (what I’ll refer to here as) “ghost codes” in some cases ... where the Tech is essentially told to do nothing but wait ... and I think it’s just “time” that makes the “ghost code” go away.

OR - maybe another “real code” is forthcoming.

Problem is - in these “Inspection States”, they’ll FAIL you for *any* Check Engine light, right? And up in MA, my former home state, they’re even installing cameras to stop those stations that used to issue new stickers anyway in marginal cases like this one.
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post #3 of 10 (permalink) Old 10-27-2019, 11:20 AM Thread Starter
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Yes, the new wheel speed sensor AC delco. I thought it was strange to have a communication code soon after replacing the sensor, but I was expecting another ABS code if the sensor was at fault again. My main concern is the EGR & EVAP monitors not completing, this is preventing me from passing inspection here in NY. From what I understand this year vehicle can pass with one monitor not complete, but not two. I already failed once due to these monitors, check engine light was not on at the time.

I no longer have the old sensor so how could I go back to the previous state, unplug it and drive around?
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post #4 of 10 (permalink) Old 10-27-2019, 12:41 PM
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Quote:
Originally Posted by a_alyte View Post
My main concern is the EGR & EVAP monitors not completing, this is preventing me from passing inspection here in NY. From what I understand this year vehicle can pass with one monitor not complete, but not two. I already failed once due to these monitors, check engine light was not on at the time.
You may have a Drive Cycle problem.
See link below for a common GM Drive Cycle that should be run, follow directions.

http://www.obdii.com/drivecycle.html
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post #5 of 10 (permalink) Old 10-27-2019, 02:44 PM
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I'm so fortunate not to reside in a region that requires emission inspections. This must be a nightmare for owners of older vehicles with marginal functioning emission systems that must pass inspection.

This makes electric powered vehicles look more attractive in these areas.

.
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post #6 of 10 (permalink) Old 10-27-2019, 04:03 PM
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Originally Posted by a_alyte View Post
Yes, the new wheel speed sensor AC delco. I thought it was strange to have a communication code soon after replacing the sensor, but I was expecting another ABS code if the sensor was at fault again. My main concern is the EGR & EVAP monitors not completing, this is preventing me from passing inspection here in NY. From what I understand this year vehicle can pass with one monitor not complete, but not two. I already failed once due to these monitors, check engine light was not on at the time.

I no longer have the old sensor so how could I go back to the previous state, unplug it and drive around?
I guess, as "rednox301" suggested, and since you've installed an ACDelco sensor, I would work the drive cycle angle (first) as much as possible to eliminate that as a possibility. Kind of annoying, though, that the system is "smart" enough to tell you there's a communication problem, but still too "dumb" to tell you exactly where it thinks it's coming from! The Helm Manual says the Tech would diagnose a problem like this by plugging into the network(s) and performing a "Roll Call" of all the modules. Well, why isn't the on-board computer programmed to do this - either periodically or on-demand ... though our big-screen dash displays that we all pay so much money for

2011 Equinox 1LT (new Jan 2011): Summit White / 3.0 L V6 / FWD / Pioneer Stereo / 18" Wheels / 138.2k miles [05-NOV-2019]

2002 Impala 1LT (new Jun 2002): Summit White / 3.4 L V6 / FWD / Cassette-CD Combo /225.5k miles [05-NOV-2019]
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post #7 of 10 (permalink) Old 10-27-2019, 09:36 PM Thread Starter
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Originally Posted by rednox301 View Post
You may have a Drive Cycle problem.
See link below for a common GM Drive Cycle that should be run, follow directions.

http://www.obdii.com/drivecycle.html
I appreciate the link. However, I came across this info from another source & have tried it unsuccessfully at least 5 times now. I have a subscription at alldatadiy.com & they provide steps to completing a drive cycle as well, it's a bit different from the link you provided, but it still didn't work for me.

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Originally Posted by garbec01 View Post
I'm so fortunate not to reside in a region that requires emission inspections. This must be a nightmare for owners of older vehicles with marginal functioning emission systems that must pass inspection.

This makes electric powered vehicles look more attractive in these areas.

.
I've had my share of vehicles & this is the first time I've had an issue like this. I drive an old '91 Accord as well & it passes because it's pre-OBD2 I guess, no Data Link Connector to hook up a scan tool. Most places just say "hey, it's a '91"! To make things worse I'm in NYC, a place bombarded with traffic agents. Park on any street & you can bet your expired sticker will get noticed. This does make me want to relocate to a region such as yours, however!


Quote:
Originally Posted by Colt Hero View Post
I guess, as "rednox301" suggested, and since you've installed an ACDelco sensor, I would work the drive cycle angle (first) as much as possible to eliminate that as a possibility. Kind of annoying, though, that the system is "smart" enough to tell you there's a communication problem, but still too "dumb" to tell you exactly where it thinks it's coming from! The Helm Manual says the Tech would diagnose a problem like this by plugging into the network(s) and performing a "Roll Call" of all the modules. Well, why isn't the on-board computer programmed to do this - either periodically or on-demand ... though our big-screen dash displays that we all pay so much money for
I couldn't agree more! I read that a faulty engine coolant temp sensor could affect the EGR system. My Equinox does have trouble starting at times when warm so I ordered a new ECT sensor which should be here tomorrow. I know it's best to test these things but the sensor was cheap enough & it's also ACDelco.
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post #8 of 10 (permalink) Old 11-02-2019, 01:12 PM Thread Starter
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Back to canbus. With the key off engine on I get 2.1v on CanLO and zero voltage on CanHi. Shouldn't I be getting around 2.5v on CanHi?
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post #9 of 10 (permalink) Old 11-03-2019, 10:52 AM
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Originally Posted by a_alyte View Post
Back to canbus. With the key off engine on I get 2.1v on CanLO and zero voltage on CanHi. Shouldn't I be getting around 2.5v on CanHi?
Didn't mean to ignore you, I don't have that info.
The info in my manuals is for GMLAN, not Canbus.
Maybe someone with a GEN I vehicle can respond.

2014 Equinox LTZ FWD 3.6L. V-6 (LFX)
GM6T70 Transmission-Gen II(M7W)
Crystal Red Tintcoat-Brownstone Leather-(FE2) Suspension-18" Wheels
Build Date: Nov. 04, 2013-Delivery Date: Nov. 25, 2013
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post #10 of 10 (permalink) Old 11-06-2019, 09:29 PM Thread Starter
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Didn't mean to ignore you, I don't have that info.
The info in my manuals is for GMLAN, not Canbus.
Maybe someone with a GEN I vehicle can respond.


No worries, I didn't take it as being ignored. I didn't realize GMLAN was different than Canbus. I look into this further on my end.
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