is this possible, alarm burn pcm?
Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=112849
Printed Date: November 03, 2025 at 3:53 PM
Topic: is this possible, alarm burn pcm?
Posted By: t&t tech
Subject: is this possible, alarm burn pcm?
Date Posted: April 01, 2009 at 4:49 PM
ok so here's the deal, installed a 791xv into a 2005 subaru impreza recently, foreign used i might add, no factory immobiliser, pretty straight forward as i've done lots of them before, no problems, the customer comes back about a week after says his engine check light is flashing intermittently, so i check it out, it's off to his surprise, he says ok, drives off, calls the following day says it's on constantly now, so our supervisor is friendly and decides he'll have it scanned for them just to satisfy their claim that the alarm is causing this, we sent in the car to two of the most reputable dealers we know, scanned by both dealers and they said something was mal-functioning with the car's PCM, so now they carried it to their own guy, because apparently they didn't trust the guys we had the car done by, the car is driving all this time i might add, the guy there did his checks and said the PCM is burnt, and says the alarm caused this, the car couldn't start at this point, then he says he changed a fuse he had found to be burnt and the car started ran and then stopped again, and now they want the shop to pay for a new PCM, the guy says the wrong ignition wire was powered which caused this failure, now here is my question, is it possible the alarm could have caused this?, if so how?, the car has two ignition wires common at one point by the way and everything worked flawlessly at the shop, and how is it that even though the PCM was burnt he replaced a fuse and it started back up?, is this possible?, i'm thinking co-incidence, do you guys smell something fishy like i do?, if anything is unclear please let me know.
Replies:
Posted By: howie ll
Date Posted: April 01, 2009 at 5:47 PM
The warning light as far as I know should have come on IMMEDIATELY had you done something wrong. May I assume you did a before and after vehicle check? If so you shouldn't be liable, does your company have any friendly relationships with Scubie dealers over here (UK) or in Florida. I have had one VW and one Vauxhall give me grief, bad running and stalling out after I connected the tach feed to an injector wire, I replaced with an inductive sensor and no further problems. It sounds like someone is trying it on.
Posted By: t&t tech
Date Posted: April 01, 2009 at 6:56 PM
yes i did a before and after check howie, and i didn't even use tach, voltage all the way, and what i don't get is how could the pcm be burnt and the car started and ran, the thing is he said it firstly only came on while he was driving, which leaves me wondering if it was that way before he came inthe shop, because i would have no way of knowing this unless i drove the car before i installed.
Posted By: KPierson
Date Posted: April 01, 2009 at 9:58 PM
There is an easy way to tell. Have the car fixed (at customers expense). Have the dealership disconnect the wire they "think" caused the problem. After a week or so of driving the car hook the suspect wire back up. If the PCM fails again you reimburse the customers for the first (and second ECU). It's definately a gamble, but I think you'll come out ahead. ------------- Kevin Pierson
Posted By: tedmond
Date Posted: April 02, 2009 at 6:54 AM
that is true, if something did go wrong, it would have thrown a CEL light. if the pcm was damaged, how could that person still drive? but in your case, i would suggest doding what kevin said. it may cost now, but at least you took the time to take care of the customer. its always customer appreciation that makes a shop reputable.
Posted By: howie ll
Date Posted: April 02, 2009 at 7:02 AM
Run with KP's suggestion.
Posted By: KarTuneMan
Date Posted: April 02, 2009 at 7:44 AM
KPierson wrote:
There is an easy way to tell. Have the car fixed (at customers expense). Have the dealership disconnect the wire they "think" caused the problem. After a week or so of driving the car hook the suspect wire back up. If the PCM fails again you reimburse the customers for the first (and second ECU). It's definately a gamble, but I think you'll come out ahead.
GAMBLE? This word don't even come close ... the suspect wire is hooked back up and you get toast again? I would be scared poopless! (it is however, the best way to investigate and solve the issue!) good luck and keep us posted. -------------
Posted By: t&t tech
Date Posted: April 02, 2009 at 4:55 PM
here's the thing, the customer doesn't want to go with the dealers we reccomended, they wanna go with their guy, who is a side of the road electrician, who was changing oil in a nissan 280c when we went to check out the place, i was like wth, so the guy originally says, we connected the wrong ignition wire, the vehicle mind you, only had one, so now he changes the theory, and says the 791xv sent a surge that fried the pcm, and we still have to pay, they refuse to believe that the alarm isn't responsible, taking a gamble with the pcm, that's a costly gamble, the cost of one is a little over 5k,
Posted By: KPierson
Date Posted: April 02, 2009 at 5:31 PM
Power inputs don't "create" power surges, let alone repeated power surges over the course of days that eventually kill PCMs. Modern day PCMs are designed to handle any abuse an electrical system can throw at them, INCLUDING "crowbarring" the battery for extended periods of time. If the PCM was fried from a power surge the car alarm would be toast also. The PCM cost 5k what (I'm not familiar with the currency in T&T)? I know that can't be US dollars. You should be able to get one for $3-400US I would think. It is a gamble, but like I said I don't think you did anything and when comparing $400 to $800 it's really not that big of a gamble. What kind of fuse is on the power lead of the alarm? Was it blown? If there was somehow a power surge that fuse would have been blown and the alarm wouldn't work. What fuse was blown that they replaced? I'm not sure how things work where you are but here we always had the right to let one of our experts inspect the car and diagnose the issue. This really, really, really sounds like an unfortunate coincidence to me. ------------- Kevin Pierson
Posted By: t&t tech
Date Posted: April 02, 2009 at 6:06 PM
the alarm was still functional when i went to visit the vehicle, locks and everything, except the remote start, since the car wasn't starting with the key, i'm not sure which fuse had been changed because i wasn't present at the time, but if if the pcm was burnt, how then could replacing a fuse result in the car starting, which is what the electrician said happened, isn't a burnt pcm gonna result in an undriveable car, and currency it's like 1u.s dollar to 6 t.t dollars kevin
Posted By: t&t tech
Date Posted: April 02, 2009 at 6:07 PM
oh and congrats on the addition to the family kevin,
Posted By: jim hunter
Date Posted: April 02, 2009 at 7:20 PM
seems odd since a subaru dealership says its not your fault its a failure with the car why would they decide to believe a friendly backyard mechanic over an authorized dealer?
oh yea so someone besides them can pay the bill
id tell them sorry but as the shop being blamed we are able to request an inspection of failed parts by licensed mechanic of our choosing and we choose a factory authorized service technician who has told you its not our fault! and see if you can get something in writing(a copy of the repair order) from the dealership to have on hand at your shop to combat the negative publicity they will try to inflict
Posted By: robertsc
Date Posted: April 02, 2009 at 8:20 PM
i would first find out which wire was the wrong one. Next find out which fuse is blowing. Next spend 11.95 at https://www.eautorepair.net/Marketing/Default.asp You should be able to determine from that if is your fault or not. The only way it could be your fault is if you tagged into the wrong wire p.s, i would avoid playing russian roulette with another pcm. The voltage surge is a bag of crap how can 12 volts produce more that 12 volts?
Posted By: loneranger
Date Posted: April 03, 2009 at 1:17 AM
robertsc wrote:
..how can 12 volts produce more that 12 volts?
A failing power supply, using a 12v source, can easily produce more than 12v on it's outputs. ------------- Ideal - cmon dude, add to topics in a useful manner, not stuff that is obvious.
Story - Phzzzt! Hey, what happened?! ... Isn't it obvious?
Moral - Never dismiss the obvious.
Posted By: howie ll
Date Posted: April 03, 2009 at 2:17 AM
Log all of this, everything germane to the problem that's been stated here and by the Subaru dealer, AND the 280c specialist, I owned one 20yrs ago till I ventilated the block! Sit the customer down OR if it has gone too far write to him stating all these known facts, send it recorded delivery or equivalent and keep a copy. If you have lawyers or insurance talk to them from the position of denying ANY liabilities. I would also word your comments/letter to him that way. In the UK the customer is obliged to inform the installing company of any problems but doesn't have to give them first repair option.
Posted By: KPierson
Date Posted: April 03, 2009 at 6:00 AM
robertsc wrote:
p.s, i would avoid playing russian roulette with another pcm.
If the customer believes his mechanic over the shop this is pretty much the ONLY way to prove to the customer that the alarm didn't cause the failure. It all comes down to how confident you are that you didn't cause the problem. If your alarm did cause the problem then this will pretty much verify you were at fault. It also depends on who is going to be paying the repair - I'm assuming it would be covered under insurance, but I could be totally wrong there. In an insurance claim a few hundred extra dollars won't be a huge deal - if the cost is coming out of pocket AND you think you might be at fault then the "try a new PCM" idea probably is not a good one. It's just important to let him drive the car for a while before hooking the alarm back up to make sure there isn't something else in the car causing the problem. If the problem was caused by a faulty alarm system (which I still don't believe) who would be at fault? I know the alarm manufacturers don't warranty anything past their alarm, even if the alarm did damage something else. If a shop installed a defective alarm properly would they still be liable for the damaged caused by the faulty alarm? I've never ran in to such a circumstance. Another thing that would be interesting to know is what exactly "burnt" on the PCM. Request that his mechanic draw out the damaged circuit - starting from your alarm connection, to the PCM, and then, in writing, have him report what circuit is damaged inside the PCM. If his response is "the PCM is burnt thats all I know" then how can he possibly relate this to the alarm install? This whole situation reminds me of a thread on here about a year ago about a guy who had a remote start installed on his van out in NY (I believe) and the van made it about 1/2 mile down the road before the tranmission failed. He, and his shop, blamed the remote start, but ultimately in the end the courts decided it was in fact a coincidence. I'll see if I can find that thread, it may be a good read. ------------- Kevin Pierson
Posted By: robertsc
Date Posted: April 03, 2009 at 10:28 AM
loneranger wrote:
robertsc wrote:
..how can 12 volts produce more that 12 volts?
A failing power supply, using a 12v source, can easily produce more than 12v on it's outputs.
and what part of a remote start or alarm has a power supply?
Posted By: KPierson
Date Posted: April 03, 2009 at 12:41 PM
robertsc wrote:
loneranger wrote:
robertsc wrote:
..how can 12 volts produce more that 12 volts?
A failing power supply, using a 12v source, can easily produce more than 12v on it's outputs.
and what part of a remote start or alarm has a power supply?
Every car alarm I've ever opened up operated on 5vdc, so there is a power supply in every one I've ever seen. Usually just a voltage regulator and a few caps I doubt it would have the capacity to damage a cars PCM though, like I said the cars ECU should be built to handle pretty much anything that could go wrong in a cars electrical system. ------------- Kevin Pierson
Posted By: KPierson
Date Posted: April 03, 2009 at 12:46 PM
t&t tech wrote:
oh and congrats on the addition to the family kevin,
Thank you! Being a Dad sure does change your priorities around a bit.... Not near as much time to play around these days! ------------- Kevin Pierson
Posted By: howie ll
Date Posted: April 03, 2009 at 2:07 PM
Ref Jim Hunter's post:- If you have it in writing from the dealer that it wasn't your fault, you should be home free. No court of law will find against you. Kevin, I find it's easier with grandchildren, I send 'em home to mum. Darren haven't turned on Sky sports yet, i suppose you're murdering us at the cricket?
Posted By: t&t tech
Date Posted: April 04, 2009 at 7:21 PM
so we decided that we aren't going to replace the burnt out PCM, we informed them that all the reputable dealers saw no possible way the alarm caused the burn on the pcm, so we let them know they would have to take us to court, so they decided they would replace it themselves, they even came to apologize for their rash behaviour towards my supervisor, i think they realized that they couldn't pull one on us, so they gave up. thanks as usual for all the help guys, it's appreciated.
Posted By: KPierson
Date Posted: April 04, 2009 at 8:23 PM
Sounds like a great end to the situation. However, now the question remains, whats going to happen with the alarm? Will it be hooked up or uninstalled? ------------- Kevin Pierson
Posted By: howie ll
Date Posted: April 05, 2009 at 2:16 AM
Great and now you're applying for a job in Westminster as a spin doctor! Seriously in any confrontation like this, pre-check, post-check, have all the facts and present them calmly.
Posted By: t&t tech
Date Posted: April 05, 2009 at 6:21 AM
the alarm is already removed, since they weren't sure of what was exactly causing the problem to begin with, so we removed it and all the wiring to eliminate it as a cause, we won't be installing it back for them though, the bad blood had already been drawn,
Posted By: howie ll
Date Posted: April 05, 2009 at 6:38 AM
This is uncle Howard being OTT (as usual). Assuming no money has changed hands since they paid for the original install, and you have the alarm, don't give it back unless they pay for the de-install 
Posted By: t&t tech
Date Posted: April 05, 2009 at 12:08 PM
wat up uncle howard, i thought you'd be heavy on the criticism, seeing the result of the series with the windies and the english, 
Posted By: howie ll
Date Posted: April 05, 2009 at 12:24 PM
Nah I lost it Spurs were coasting to an easy victory over Blackburn when their Columbian got his marching orders, then they lost 2-1. Also 20+ vehicles on a tracking job put off for 2 weeks. Why does everyone have to bugger off over Easter when I need to work and earn money? Guess what tomorrow I've got one of those nasty "Chinglish R/S jobs on an 02 Corolla* and he doesn't want to spring for a by-pass. I've already told him there's NO product warantee. * Ain't called a Corolla here anymore, its an"Auris" in western Europe and made in Derby, yes can almost see the Trent Bridge where the Cricket ground is. I was up there working in August.
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