I think I have a problem with my ECU. The other day it wouldn't start. Nothing, no noise at all. I pulled the power wire off the starter and measured the resistance of the wire (red/Yel) to ground and it was 197 ohms with key off - strange:-\. So I hooked the battery directly to the starter and it started right up! So I figured I had a short in the ignition wiring. I eventually found a Red/Yel wire that went to the ECU (MPFI control unit) which was causing the short (~197 ohms). I disconnected the ECU from the connector and the short went away. I cut the wire to the ECU and connected everything back up and it will start, but it has trouble starting when cold. Not sure of the function of this input to the ECU. Anyone suggest a fix? Can someone with a similar engine check to see if they get ~197 ohms to ground on their starter wire with the key off?

 

Car has 136,500 miles, Automatic Transmission, EJ25 DOHC engine.

Edited February 23, 200917 yr by mags

How long has it been doing this? Did it just happen?

Just happened. Was working fine prior to that. I did leave out that the battery was dead as well. Don't know how they are related since the battery wouldn't see the short with the key in the start position. I think I left the internal light on.

So it never occured to you that the solenoid contacts in the starter can be bad?

 

By no noise do you mean no cranking?

 

Why did you not think the starter/ignition switch is bad, since the ECU has ntohing to do with the starter engaging.

 

If the ECU was bad you would have bigger problems, so I am not convinced thats a issue. Right now thats like assuming since your foot fell asleep you had a stroke.

 

 

nipper

The R/Y wire going to the starter solenoid should tie to the inhibitor switch, not the ECU. I can't explain why the resistance changed when you disconnected the wire to the ECU but that should not be the same wire that ties to the solenoid. Check the resistance between those two wire ends. If they are the same wire the resistance will be real low.

 

Power from the ignition switch should go to the inhibitor switch and then to the solenoid. Perhaps there is a problem with the inhibitor switch causing the trouble.

I'm looking at a diagram of the ECU wiring for a '97 Legacy (I assume the '96 is similar). The R/Y wire from the inhibitor switch contacts that close in Park/Neutral is shown connecting to a pin on the ECU. On the starter circuit diagram, the same inhibitor switch contact (and R/Y wire) goes to the starter solenoid. It would seem that since one cause of a P1507 code is the ECU not knowing when it's in P/N (http://endwrench.com/images/pdfs/DiagTroubSum04.pdf), that wire might be going to the input that allows the determination.

 

As to whether the 197 ohm measurement explains the 'no start' condition, I'm less inclined to think that. As Cougar suggested, the inhibitor switch might be the culprit. Also, bad contacts in the starter itself are pretty common.

Edited February 25, 200917 yr by OB99W

If it happens againe, put the car in neutral and see if it starts.

 

If it does its the inhibitor switch, if it doesnt its hte starter contacts.

 

 

nipper

 

As an interesting PSA, more and more new cars are mking the ignition switch more like a key operated "boot" switch. I've been seeing more and more owners manuals stating "to start the car turn the key and release, do not hold the key. The engine will continue to crank for (insert time here) untill the engine starts".

 

I wonder how many people realize this.

As an interesting PSA, more and more new cars are mking the ignition switch more like a key operated 'boot' switch. [...]

So if the engine doesn't start, how long before the ECU cries 'uncle' and automatically has OnStar call a flatbed tow truck?

So if the engine doesn't start, how long before the ECU cries 'uncle' and automatically has OnStar call a flatbed tow truck?

 

 

heheh well (yes forgive me i plead tonka toy lust) i was rading an 2008 Jeep manual and it said on the auto it will crank for three seconds. The manual did not have that feature since you can start it in gear if you need to get unstuck.

 

nipper