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Chevy avalanche 1500: Northface - ABS Alarms on Bumps

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Sorry if I have messed the text up on here. I may have cut and past the info in two parts of your online form.

 2003 Chev Avalanche 1500 - Northface - ABS Alarms on Bumps. Doors lock and unlock


Hi there, you guys have been able to help out in the past so let’s try again (Vehicle: 2003 Chev Avalanche 1500 Northface 5.3L Automatic Custom tune flashed at speed shop with header install.


Current problem, about a month ago had an issue where hit a bump (pot hole) and received an ABS alarm and door locks locked and unlocked. Pulled over, shut down, started and went away. Checked with the Diablo Predator for DTC codes – none – use the Diablo for codes only as the custom tune has been flashed.


We had been through about a week of solid rain and it was very wet. Occurred a couple of more times and one time actually powered down the truck. Only happens on pot holes. Speed bumps and curbs are not an issue


Wiggled the ground wire on the back of the head, went after some serious bumps and holes that day and no issues. Fine for a few days then came back. Today I pulled the ground wire from the firewall, cleaned the lead and brushed the rust of the bolt back to steel and reattached. No issue on bumps. Hit a hole – instantly back.


Checked what I believe is G103 and G104 under the driver seat (frame) and they are rusted and wiggled. No change. I tried to pull the 60 amp fuse but had alarms so it was time to contact you guys. ABS pump is not running when truck is off. Almost lilke something is loose as only on a hole and intermittant. Not sure but maybe the Caliper connect or harness is loose but it seems fine from a visual inspection.

Welcome to just I'm here to help you and your 100% satisfaction is my goal.As for the ABS checked to see if there's any trouble codes being stored in the memory of PCM , possibly you have a faulty wheel bearing or wheel speed sensor or speed sensor connector, as for your door locks this really seems to be a faulty body control module, try squeezing are banging on the body control module and see if the door locks activate
Customer: replied 6 years ago.

Couple of questions:

1) where is the body control module located on the Avi?


2) I will have a look at the wheel bearing tomorrow and let you know what we find - I saw a few threads on line that pointed to bearings - I cant recall when I changed them last - probably 50k km ago. I do use the truck off road so that could have put some where on it.


3) TSBs and various forums were pointing to to a ground leak off the ground strap - do you have any experience with this or have you seen it before? The wiggle and clean took 90% of the issue away. The G103 and G104 ground straps under the passenger side seem fine - I have penetrating oil sitting on them and will pull off tomorrow and brush clean.


4) I saw something about the wheel speed sensor - if I recall it is basically the ABS sensor - correct? I cant see it being the module as there is no noise from the pump and it would happen on all breaking just not bumps.


5) the diablo is not pulling any error codes. I will check it again tomorrow am.


Trying to avoid taking it in to the dealer. Electric issues can get very pricey just to diagnose let alone swapping parts.


Appreciate your help.





The body control module is located under the left side of the dash below the steering column, problems with the wheel bearings and the wheel speed sensors are both one in the same an yes they do affect the ABS
Customer: replied 6 years ago.

thanks I will look - meant Driver side for G103 and G104. any experience with them?


Will also look at the sensors when I have the truck up tomorrow. Prior to the spring rain we had a pile of snow and ice (about two weeks prior - welcome to Alberta!) some snow or ice may have also lodged in the sensor harness. On the sensor how can you tell if it is shot or is it a low cost fix to just pull and replace - manual seems pretty straight forward to replace then.





With the censors what you need to do is monitor the wheels speeds on a scan tool as you're driving and see if any particular wheel speed is different from the rest
Customer: replied 6 years ago.

Just trying one more thing so you have a full diagnostic of all that we have done for future reference. In summary over the past coupld of days


- checked bearing - fine

- regrounded G103 and 104 - helped - still issued on the left side

- I spoke to Onstar and GM and there are no trouble codes.

- we have isolated to the right front - we believe - on pot holes on the right side we are seeing speed spikes on the spedometer


We are about to pull the right front sensor and check it as well as the wiring harness.


To replace is about $35-$60 for the part up here


Will advise.



good let me know what you find thanks

Customer: replied 6 years ago.

update: swapped out the sensor - no issues - bonus - made it 200 yards hit a bump - no alarms - doors unlocked - this after I had the doors on manual auto lock


Reduced power came on - pulled over, code P1518 - TAC module - cleared, restarted and made it 200 feet - complete shut down and would not start


Towed home and on route had the electrical system fire back up - started reduced power light on - limped home - parked - Onstar no additonal codes. Parked and was going to take to the dealer this am


would not start again. not even turn over


so spoke to the forman at the dealer - he says low voltage. Now re-re-attaching all connections with diaelectric grease.


Will advise - what a saga



Check for poor connections and open wiring at and near the Throttle Actuator Control Check ground G104 on the rear of the left cylinder head. Check that the latest engine diagnostic calibrations are programmed into the Powertrain Control Module.

Customer: replied 6 years ago.

had it running this am after sitting disconnected all night. Put new post screws in - fired up first time - error codes, erased, ran stopped 3 times and then fine let hit temperature - fine - then pulled battery to bench test at local shop - seemed fine - put in - dead again will not start. Had cycled 10 times no issues before pulling and replaing battery. Dealer pointed to battery connections not related to P1518 - her was right but now toast. Door locks dont work unless key is in the run position, seat belt light stays on even with key out CD player not working


This is getting weird. I am officially at a loss




so is the p1518 back?
Customer: replied 6 years ago.

it wont turn over so I can't tell. The 1518 was there - then when cleared it never came back.




Check for 12v on the CRANK fuse in the under-hood fuse block when attempting to start. Try moving the key cylinder again when the vehicle is a no crank. If moving the cylinder allows engine to crank, replace the ignition switch
Customer: replied 6 years ago.

thanks I will try it before pulling the starter. thinking about it we have had isses where the ingnition key would stick on occasion.


Appreciate the insight - will keep plugging



ok let me know thank you
Customer: replied 6 years ago.


- checked crank fuse in crank position - barely pushed 2 volts

- replaced ignition switch - now pushing about 5-6volts

- secuirty light on - read on the web that the system has to relarn the security code in the new ignition switch (battery was also only sitting barely above 12 volts)


- retaining the system - crank, leave in run then wait for light to go out then off 4-5 seconds and do this 3 more times.


Also have the seatbelt light flashing


Will keep you in the know - what a bugger this has been

Side note no clicking at the starter relay - have swapped it with others in fuse box (Same part number) - no change - will see what happens




Checked the voltage at the ignition switch itself possibly we have a faulty connector at the ignition switch or a faulty power distribution center also make sure the batteries fully charged
Customer: replied 6 years ago.


- boosted the truck and brought battery back - was low with all the testing

- checked and at Start - crank fuse was pulling 14V

- no noise from the starter relay

- checked pins 30 and 85 - both pulling 14v but no noise


Tried to make it to the part store before they closed and will have to try tomorrow. Want to put in a new relay even though we swapped out the others with no luck.


Then with new part will continue down to selinoid/started and see if we are pushing to there


Truck looks like it was hijacked. I have to remember how to put it all back together. :)




ok let me know what you find
Customer: replied 6 years ago.


this is absolutely bizarre... sequentially:

1) pull negative lead then re-attach

2) door locks open with the remote

3) run, stop, security light on and sat now for almost 30 minutes and is not going out

4) door locks do not work off fob or manually in the truck


repeat 1-4 and I noticed that the secuity light (vehicle and lock) on the dash do not appear at crank, only when I let it sit at run


Is this normal? Also pulled that body module we spoke about a week ago and reset and insprected for damage - does not apprear any.


Also checked all fuses again in particular PCB B as that was noted an issue on the web.


I am really hoping it is not the starter, with the headers in there it is going to be a nightmare to remove. Starter is cheap ~ $125 but the labor will be brutal especially if they have to pull my headers


Hitting a wall - have you ever seen anything like this?




If the security light is remaining on while trying to crank the engine then this is most likely going to be a security problem do you have power down too the starter?
Customer: replied 6 years ago.

we are checking


Customer: replied 6 years ago.


The terminals for the starter are behind a heat shield that is only accessable when the starter is removed. We tried one last time to rotate all the relays throgh (Same part number) and they all work in park lights but not in the starter relay block.


I also checked my manual for any fuse relating to the security system (VAT) and the the passive key lock and could not see anything.


Seems to make sense that something has gone wonky in the security as when the batter is reset then the fob works. Works right up the point of a crank test then nothing.


The crank and sit for 10 is not doing anything.






does the security light is remaining on while trying to crank the engine
Customer: replied 6 years ago.

-the security light is NOT on when cranking - only when I let it return to Run or pull the key

-battery was also down to 5 volts this am so something is drawing on it

- starter - jumped pins 30 to 87 on the relay and the starter cranked so it is not the starter

- tried one more thing - jumped red and pink wire at the switch and replaced the starter relay with the AC relay to double check

- will not crank


With power to pins 80 and 30 we know that the relay is getting power and jumping the relay the starter works


has to be something with the secuirty system


any ideas?

Customer: replied 6 years ago.

why did you close this one? How do I get you paid then? Is it because I reached out to another expert that helped me in the past? I tagged him out of curiosity as he has a 2004 Avi.


Let me know - intent was not to upset anyone or go astray



If you have power two the starter relay when turning the key to the start position possibly the PCM is not grounding the relay properlygraphicgraphic

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