mjrav

Any help with this is greatly appreciated.

The check engine light has been on for some months with a code of P0601. "Internal control module memory check sum error"

The car could not be running any better. The light is the only issue.

I reset the check engine light three times and it comes back on in `12 to 80 miles.

Is the ECM necessarily bad and needs replacing or is there some other option.

Where in the car is the ECM? In the passenger seat back?

Thanks,

Mark

Hey All, good day. I have a 91 lexus ls 400 and it drove fine until the summer came thru. I noticed that when i turn the AC on and drive it for about 45 mins in 90deree weather, the car starts loosing power. It starts jerking forward and backwards and sometime stops. But am always able to start it up and keep moving with continues jerks and the rpm revving up and down.

This only happens to me in extreme heat with the AC on. If i drive my lexus without the AC it is fine.

Please advise.

thank you

Hi,

I've been experiencing similar problems with my 91 LS400.

I had a diagnostic check done and there were indications of an igniter problem.

I haven't cured it yet - it's intermittent - seems temperature related.

Today I put a plastic bag of ice on the igniters and in a few minutes the problem went away. Then later, in the heat of the afternoon, the problem never came back......?

Thank you for all the help. This forrum is wonderful.

On the way home from buying a 1991 LS400 - 114k miles - the O/D light started flashing and the trany forgot that it had more than 2 gears. I was sick. There went my good deal.

I looked at several posts on this subject and then had the tranny flushed. ($190 at Toyota dealer)

All the problems went away in the next 20 miles.

Thanks again to all that contributed. :

Try pulling all the belting out of the retractor looking for twists and tangles.

White is normaly water vapor.

Was the engine and exhaust system completely warmed up?

Has your coolant level been decreasing abnormally?

Look for bubbles (exhaust) in the coolant resevoir with the engine running.

This is a leaky gasket.

Check that there is no oil on the drive belt / pulley and proper tension.

This can cause slipping when under load or hot.

My 90 LS has had a tick, tick, tick from the speedomet (or cable) for the last 100,000 or so. It has never seemed worth fixing and doesn't bother me at all now.

I had a brake job done at Lexus once.... $1000 or so.

They said it was their policy to always replace rotors.

I had to replace mine two years ago.

I remember it was a tight squeeze and the alternator had to be at just the right angle to fit. Almost a Chineese puzzle but it went.

I had a similar thing years ago.

That one required the engine to be reved up several thousand RPM in order to get useful voltage. It wasn't very practical.

This "dimming" may be normal. Don't overreact and fix what isn't broke.

When you step on the brake it's normal for the engine to idle slightly slower resulting in slightly less alternator voltage. There may even be a flicker in the lights as this occurs. Mine always does - been working the same way for 140,000 miles.

Much of the white smoke seen when cold is just water vapor. Look at anybody's exhaust until the whole system warms up.

The smell and poor mileage is another problem. My 1990 LS400 with 200,000 mi. normally goes around 400 mi between fillups with mixed driving conditions.

I just went through this. LS400 200,000 miles.

I took the coolant bypas pipe off but had to break the wiring cover off to do it.

My starter was'n disengaging either. The contact disk tilts due to the heavy wear on one side. I built up the worn contact with silver solder. Filed it flat again - probably better than new. The brush compartment needed cleaning also and some fresh grease on the gears. Don't loose the 1/4" dia ball on the end of the solenoid shaft.

I defy anybody to get the starter out the back. The firewall is only a couple inches away. I took the intake off.

I just went through a similar problem with my LS400 200,000 miles.

I turned the two front rotors twice on my lathe. Each time the problem went away for awhile then came back. Nasty shake at off ramp speeds mostly in the steering wheel and brake pedal. (While braking)

I purchased one new rotor for worst offending RF wheel and problem is gone.

I think it's a GLAZING thing causing uneven friction. At certain speeds the brake lines telegraph these pulses through the system agravating the problem. That's why you feel it in the pedal so much.