Does anyone know what lack of a 1-2-4 code in diagnosic mode 2 means?

Per FAQ, I'm trying to solve a hunting (but smooth) idle problem and Test Mode 2 fails (I think) the 1-2-4 Engine idle speed compensation for Automatic trans. test. The IAC is nearly new so it's likley the ECU is in control of the idle problem. The ECU gives 1-1-1 (no fault) but I do not get the proper response from moving from Drive to Neutral (1-2-4). Is the IAC supposed to increase idle soley based on selector level position? (I was thinking of repalcing the TPS pot.)

Any help would be appreciated. Anyone trouble-shooted a LH 3.1?

TomM

I've got a '90 244 manual with LH3.1, so I acquired some wiring diagrams. I can't help with your problem though...not a clue how to approach that with testing procedures.

http://mason.gmu.edu/~mtowery/92Volvo240LH3%B71-page1a.jpg
http://mason.gmu.edu/~mtowery/92Volvo240LH3%B71-page2a.jpg
http://mason.gmu.edu/~mtowery/92Volvo240LH3%B71-page3a.jpg
http://mason.gmu.edu/~mtowery/92Volvo240LH3%B71-page4a.jpg
--
forums.turbobricks.com

Thanks Michael. Those diagrams add to the one in my Haynes manual. The gear selector switch is a likely culpret.

TomM

No help here (yet), but the 1-2-4 code isn't unique to your LH 3.1. So far I can't find the input signal to LH 2.4 or Regina ECUs in my '93 greenbook diagrams. Yet the fault tracing manual does describe the 1-2-4 code you mention.

I'll check back when I find something. Should be a signal when selector is not in P or N.

OK, I'm back, with good news and bad news.

GOOD: Fault Tracing book says the ECU pin is #30, with input from:
"Start Detent contact (automatic).
Information about gear selector position.
Used to maintain constant idling speed when a gear is engaged.
No signal voltage [if] in P or N. Voltage [if] in D-1-2-3-R."
If no signal (Mode 2), idling speed drops when a gear is engaged".

BAD: The only inputs to pin #30 on LH 2.4 and Regina diagrams are either:
• Ignition Sw 50 (Cranking voltage to starter)
or
• Service Socket (Underhood jumpered voltage to starter)

Can't find anything coming in from "Start Detent Contact" at all. And any voltage at that point, would feed right back to the Starter Solenoid. So maybe this IS unique to LH 3.1, and there is a glitch in the documentation (not unheard of).
--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Thanks Bruce. (Is your '93 940 a regina? Mine's a Calif. w/ EGR.) I think that establishes that the ECU is looking for a voltage from the gear selector and I need to re-do the check. I followed the FAQ and cycled thru the N to D. I'll need a helper (don't trust hand brake), but I'll try leaving it in drive and see if the code comes thru correctly or not. If not, that could be the problem.

Unfortunately, the unstable idle seems to occur in drive, but like spook implied, an intermitant connection can cause funny things. It looks like I have a weekend project.

TomM

Dear TomM,

Good p.m. and may this find you well. According to the Volvo Pocket data booklet - cars (700,900,S90,V90,850), 1991-1998, p. 240,
Fuel System (A2), Mode 2, Code 1-2-4 = RPM compensation for transmission OK.

I do not pretend to know what, if anything, should be done in response.

Could the IAC, although nearly new, be dirty? Could it have a slightly corroded connector?

Hope this helps.

Yours faithfully,

spook

Thanks spook - especially for digging down thru the other posts. I think I'm on my own here, the LH 3.1's aren't too common and I don't have the factory manuals. I'm having idle trouble (though smooth) so it's likely the auto transmission compensation is faulty.

My best guess is the ECU checks to see if the selector is in neutral or drive and somehow that's defective and therefore I don't get the correct code. (Though the FAQ aren't 100% clear how/when that code will appear.) I'll try wiggling the gear selector and see if it helps.

If I fix it, I post so other know the story.

TomM

Dear TomM,

Good p.m. You're welcome. You need to get the wiring diagram manual for this car (go to www.volvotechinfo.com , the official seller of Volvo manuals).

With the diagram for the engine control unit, you can trace the wire(s) that take the transmission signal to the ECU. A microscopic bit of corrosion on a connector or contact may have cut the signal. Clean the connector or contact, and everything could be fine.

Without the wiring diagrams, though, you're shooting in the dark, without a night-vision scope or tracer ammo.

Hope this helps.

Yours faithfully,

spook