: Mechanic's Help Needed with Electrical Question

05-04-05, 09:48 PM
Just when you thought I was going to be quiet about all of this, I'm at it again. I need someone with practical, professional experience to tell me if, by a preponderance of the evidence, it is probable that Car Toys caused the issues I'm having.

In case you missed the adventure, I'll outline it below:

I purchased the car not long ago and drove it happily, getting about 15 MPG around town.

I had a stereo installed at Car Toys, then an alarm about a week later

IMMEDIATELY upon starting the car, the install tech noticed the Check Engine light was on but assumed it had been on previously. This was not noted in their paperwork though the tech admits to noticing the light right away.

During the next week I discovered that the ALDL port had stopped working, my mileage had dropped to 9 MPG and I experienced problems with my automatic transmission. I made Car Toys aware of this and they checked their wiring, etc., and discovered that yes, the ALDL wasn't working. They stated, more than once, that if they inadvertently did something wrong, they would pay for any repairs. The tech said he'd replaced the vehicle's ground wire and relocated it as the old one seemed inadequate.

Subsequent diagnostic testing revealed that the ECM had been disconnected from the fuse panel and was not powered. The mechanic cannot determine when it was done or why, but it appears very unlikely it was done for any beneficial purpose. Nothing else had been modified which would indicate someone was trying to circumvent the ECM on a permanent basis. The ECM was reconnected but gives indications that it may be malfunctioning.

The previous owner talked with his mechanic and while the mechanic cannot recall specifically testing the ALDL, he notes that I'd most likely have experienced these problems all along.

The alarm has an ignition cut-off, remote keyless entry and a relay for my power trunk. Is there anything that Car Toys may have done to short out the ECM without damaging other electrical components? During the process of reconnecting, remounting a ground wire, could something have been done improperly as to cause a malfunction? In an effort to cover their tracks might they have disconnected the ECM hoping I'd not catch on or be able to prove any wrong-doing? I have experienced no other issues of which I'm aware; all problems seem to be related to the ECM or sensors. Further diagnostics will be performed but I cannot afford to throw good money after bad.

Theories, ideas welcomed, but please have them rooted in a foundation of experience so that I may use them in my talk with the Car Toys manager. Thank you in advance!

05-04-05, 10:28 PM
The only way I can think of that they may have damaged an electrical component while installing the alarm or radio would have been by not disconnecting the battery. However, installing either does not require getting anywhere near the ECM. I'm at a loss.


05-04-05, 10:48 PM
Thanks, Brian. I should say that the ECM was disconnected from the fuse panel and the fuse wasn't there when my mechanic discovered the problem. He had to re-wire the ECM to the fuse panel and install a fuse. I'm not sure if the power wires were missing or taped out of the way or what...that's information I could use from him.

I don't know if I really believe Car Toys went to the trouble of disconnecting my ECM but all of this went down right then so what else am I to believe? If they had the key in the "On" position, the ECM would be activated, I think...so perhaps they had the key in the "On" position while they were disconnecting the battery and they didn't notice it. The put little clips on the door pins to stop the warning ding, so it's possible that they forgot the key was in there. It's tough to disconnect those batteries because of the side mounted connections and confined space. What's even more difficult is reconnecting the cables; often it'll spark and make a connection only for a moment while you continue torquing the wrench. I wouldn't THINK that would screw anything up but what do I know?

05-05-05, 08:23 PM
Any other ideas or theories out there?

05-06-05, 08:32 AM
I just find it odd that the check engine light is on with the ECM disconnected. Never tried it to see if the driver defaults to "light-on" if it receives no signal from the ECM but somehow I doubt it. I'd sure be guessing that the shop disconnected it. The problem is that any shop that would just disconnect an ECM like that is highly unlikely to be able to help you in diagnosing your current issues. I'd say you need another shop to give you some input on the matter. The problem with that is going to be getting anyone interested in fixing someone elses mess. Most shops will shy away from it. I know this isn't what you want to hear but I'm trying to be straight with you.

05-06-05, 02:38 PM
Yes, the driver does default to light on. There is a different fuse on the SES driver line. Had mine go once, lost a lot on my dash and didn't realize it. the fuel gauge was the clue, it got lower and lower and never came back up.

It almost sounds like they accidentally cut the wrong wire somewhere and hid it in a harness. Or tied into the wrong line. Does the ignition cutoff actually work? Test all aspects of the alarm. I would expect it to be tied into the HEI B+ line.

05-06-05, 05:36 PM
If it does default to "light on" then the shop HAD to have disconnected the ECM since the CEL didn't come on until AFTER the install.

05-06-05, 06:14 PM
That's my thinking. The light is controlled by a lamp driver module. The ECM can ground the light circuit, causing it to light OR the lamp driver module can do the same, in the event the computer is inoperable.

What I'm wondering is, how can I tell if the ECM is malfunctioning? I get no codes but with my mileage down and the late-shifts, I'm thinking the only common denominator is the ECM. A bad torque converter clutch wouldn't explain the poor mileage as around-town driving is mostly fine. It's not like I'm on the highway a bunch, in 3rd or 4th gear (no OD). The ECM can throw a code to indicate that it is malfunctioning, but again, no codes.

My knock sensor may not be functioning, either, though I've not had any problems. We weren't able to trip the sensor by tapping the engine block. Perhaps the ECM is failing to recognize the sensor input. Perhaps the ECM is failing to regulate my fuel efficiently...and it could certainly explain the improper shift points.

What say you?