red13

My 2001 RX300 FWD has the VSC + Trac + CEL on with error codes p0765 + p0171 + p0174. At first it was just the p0765 which was a shift solenoid D malfunction. I replaced it and after a day, the code came back. I then took out the valve body and clean that and soaked all the shift solenoids. I changed the spark plugs at the same time. The code came back again, but this time with p0171 and p0174 which is engine running lean. I took my car to transmission specialists and his $10,000 snap-on scanner that looked more like a mini laptop only picked up the p0171 and p0174 (lean) codes and didn't even picked up the p0765 code (shift solenoid) while my cheapie $30 scanner picked up the p0765 code also. He said that the transmission is fine and that the ECM is causing the VSC + Trac + CEL to come on. He said that the rx300 has a history of bad ECMs. I'm not sure what to believe. He didn't charge me anything to diagnose the problem since he only do transmissions, so he has no reason to lie about it. Is there a way to test to see if the ECM is bad?

Thanks

gazi001

Welcome to the club. For codes, P0171 and P0174 comes for following reasons according to experts:
1.injector blockage
2. dirty air filter (that is a big one)
3. dirty PVC filter
4. IACV blockage
5. gas cap
6. Exhaust pipe leak (right around the manifolds off the engine block, usally a hairline crack can be seen
and finally though probably lesser so, A/F sensors both bank 1 and 2 ( Mechanic could see the out put ratio of sensors with advance scanner.).

hypervish

The RX300 does NOT have a history of bad ECM's.

red13

Then why does my cheap scanner picks up the p0765 code while his more advance scanner doesn't?

carguy07

I think the question is, why does an advanced scanner not picking up a tranny code mean that the ECM is shot?

Lexmex

What's the type of scanner being used (brand/model)?

red13

I'm just using Autel MaxiScan MS300

http://www.amazon.com/Autel-MaxiScan...9384613&sr=8-1

and from pictures of his, looks like a Snap-on MODIS? see attachment

Lexmex

I have the same little scanner from Autel.

Any time I do something where I clean or change something out mechanically/electronically to deal with a code or maintenance like spark plugs, I disconnect the battery and let the system reset.

I'd be interested to see if after doing this, if the P0765 shows up IMMEDIATELY after when you turn on the vehicle.

Bad ECMs are an extreme rarity on these vehicles.

red13

I disconnected the battery and after a half hour of so, the p0765 code came back.

Lexmex

Did the other codes also show up?

red13

Yes, I'm not worried about the lean codes because I took out the PVC valve and it looks pretty bad and will be replacing that later today. Also will clean the MAF and replacing air filter.

Lexmex

Also the IACV should be cleaned.

With regard to your P0765, there's two possibilities, the first is that it could be stuck in the open or closed position and two something in the value body around that are is blocking it even partially. The ECM does not factor into this.

The thing that is a possibility here is that even though everything might be clean from what you see on the valve body and in the valve itself, the fluid could still have something in it causing the issue to pop up. The resistance for that valve is 5.1 to 5.5. The positive would go on to of the solenoid connector while the negative would go out on the tip of the little hole on the side in order to measure it using a 23W bulb.

red13

The manual for Shift Solenoid S4 (which I think is the solenoid D equavalent) shows a resistance of 11-15. I tested the resistance and it is within specs. Is the S4 valve not the solenoid D? I basically dropped the pan and refilled with fresh fluid 4 times already. Went thru about 20 quarts of fluid. Could it still be dirty enough to cause the p0765 code?

Lexmex

The only other thing that could be an issue is an aftermarket part. I really can't think of anything else offhand that would be throwing this code.

Which manual are you looking at, the Lexus repair manual?

red13

The solenoid I replaced it with is OEM from Lexus. Yes I am looking at the Lexus repair manual.