240 check engine light....

The "check engine" light just came on today during the drive home. I pulled
over, checked for any obvious loose wires, etc, but found nothing. I used
the diagnostic connector and found that it gave me a 2-3-1 code, which
supposedly means "fuel system compensating for rich or lean mixture at
cruise". I cleared the code and restarted the engine, but the "check engine"
light stayed on. The car seemed to drive normally, no loss of power or
acceleration, and the temp gauge stayed at its normal position. The car is
'89 240 wagon, automatic, with about 210,000 miles showing. I've owned it
for the last 40,000 or so, it passed the emissions test about 6 weeks ago
with completely normal numbers, and the O2 sensor was replaced about 10,000
miles ago. Any suggestions what I should check next?

m9876c at yahoo dot com

 

My '89 did much the same thing and the shop diagnosis was
the air mass meter.

With a new one, the car runs quieter and maybe a little better
power-wise.

Allan Ballard

 

some additional information....

Checked all wires and hoses, everything seems secure and intact. Measured
the AMM heater pins, correct resistance. SAme with the O2 sensor heater.
From past experience, I know that if the AMM is disconnected, the car is
almost impossible to start, yet this morning it started easily when cold,
and ran fine last nite on the way home. Granted, that's not a guarantee that
the AMM and O2 sensor are good, but it seems to clear them of blame for now.


The manual mentioned "low fuel pressure" as a cause. Both pumps and the
filters were replaced about 1.5 years ago, and if that were the problem now,
I'd expect to have lost power on acceleration last nite, which didn't
happen, even when going uphill. Similarly, if there was a fuel delivery
problem, like a failed injector, I would have noticed the loss of power.
Same with ignition (Plugs and wires changed a few thousand miles ago)


I cleared the 2-3-1 code this morning before the cold start, and the "check
engine" light never went off after starting the engine. Seems that if it was
actually sensing a rich or lean situation (say, from a stuck injector), it
would have taken a few minutes for the system to realize it, so the light
should have gone off and come back on later.


Any other suggestions?... Car is perfectly drivable, I just don't want to
damage anything if it can be avoided.

 

If the MIL doesn't go out when you reset it, there is another code in
memory. Memory will hold three codes. Once the test point returns a
1.1.1 code the light is out and memory is reset.

Usually 2.3.1 sets with 2.3.2 and 1.1.3 which would indicate a faulty O2
sensor. By itself the O2 sensor is likely seeing a vacuum leak (split
PCV hose) or an unmetered air leak (split, perforated bellows hose).

Bob

 

hmmmm.... I'll take another look tomorrow morning, to see if I might have
missed a source of air leak. Other than that, it sounds like you are
thinking along the lines of the O2 sensor. If I have a choice between that
and the AMM, I'd go with the O2 sensor... relatively cheap and fairly easy
to change! (of course, the AMM is really easy to change, I've had it out
when replacing the air filter, but from what I understand, it's far from
cheap!)....

 

I kinda have the same problem. My 1990 240 has a check engine light that comes on for about 2 - 3 min and then goes out, I just replaced the MAF because of 2 codes 113 & 232 (run shitty, but when I disconnected the MAF it ran good). Anyway, after clearing the codes, the check engine light did the same thing 2-3 min, but no codes yet. Wanted to mention that I can't seem to clear the codes with the diagnostic probe, but only if I disconnect the battery or even easier pull the fuse on the ds firewall. Any suggestions?