lw300 brakes

Brakes are still fine now but last night noticed that the ses was on again and the TRAC light was off. Right after that my friendly (fienldy?) constable pulled me over for a brake light out. Was the usual crud with the darn tail light design - the lamp holder was not making correct contact to the base assembly. Just rocking the lamp holder slightly made the light come on again. Until the recall is done on the tail light assemblies, I just tied a string to one of the mounting studs and to the lamp holder to c*ck it slightly inboard. Next engine start, the TRAC light came on again as normal. Could be that there is some connection between a defective brake light and the TRAC light. Neither the owner's manual or the service manual says this though.

I borrowed a scan tool this morning to check if there were any stored codes. I only checked the generic codes (should have done specific codes but would take me an hour to figure how to get to them on this multi-kilobuck tool). Got P0171 and P0174 System too lean bank 1 and bank 2 respectively. This may be a vestige of the fuel filter I replaced the other day. My friend at the garage said that it was most likely the MAF sensor or a vacuum leak. I didn't hear any vacuum leaks so have to find the PCV line and check the valve. The scanner indicated that the car is driveable so I cleared the codes and will check again in a few days. The ses lamp had gone off by itself on the way to the garage this morning. I have 67000miles on the car now.

I hear the MAF sensor can be cleaned with brake cleaner or electrical cleaner. It's delicate and expensive. Anybody have recommendations?

I believe the TRAC system is essentially part of the ABS system, so if there is a fault in the ABS, maybe that is why the TRAC system goes down. Does it turn on if you press the button? I am wondering if the rear brake lite is a red herring and you actually have a fault in the ABS too. Brake sensors clean?

Initially, the light on the TRAC button went out by itself and could not be turned on. It would come on for a couple of seconds at key-on and then go off. I had pulled the controls B+ fuse to do a reset of any faults and the TRAC light stayed on. It has gone out several times which is why I started to look into the brakes. I did pull the rear brake sensor connectors and re-seated. Did not pull the rear rotors to check the sensors. When you ask, are the brake sensors clean, are you referring to the connectors? Afik, the sensors are 'gear tooth' hall sensors...hmmm, now that I think of it, the sensors are probably magnetically biased and might attract rotor dust. Probably a good idea to pull the rotors and check. Thanks. Oppie White Plains, NY

2001 LW300 Bicycle

I don't know about the Saturn specifically, but I'v recently had a crash course in ABS-ology with my Jeep. The sensors can accumulate dust, both ferrous and anything that can stick with humidity. Another thing to check is to make sure the gaps are still in spec.

Dana

So far, so good. After clearing the codes with a professional tool - this following changing the fuel filter an oil change, new tank of gas and fixing the stuck rear brake pads - no new codes. I put on 50 miles yesterday and expect to put on about 120 today. I'm going on vacation Thursday and wanted to be sure that we don't get stuck. Think that I'll pull the rotors when I get back just to have a look-see. Oppie

Just got back from four days in the mountains of Vermont. Put on almost 500 miles and averaged close to 30mpg! Got to love highway driving. ABS/TRAC/Brakes were all great on the trip. No SES or anything until... I am two miles from my house on the return trip. Read out the code this morning and got 'Lean Bank #1' P0171. Did not also get the lean bank 2 as did a couple of weeks ago.

Can anybody shed any light on how the car knows of a lean condition in one bank? I don't especially care to run out and buy a new mass airflow sensor. The vehicle is otherwise running nicely.

There should be a list out there somewhere that details the various engine management strategies and the self diagnostic strategies. Would be helpful in understanding any faults. Just like last summer when I got a 'evap canister large leak', the last place I looked was the canister. I looked first at the seal on the gas cap and then found the actual fault in the vent solenoid that was stuck open... Now that I think of it, the service manual has some data on this. Got some reading to do now. Oppie

2001 Saturn L300/LW300 DTC P0171 Circuit Description

A closed loop air/fuel metering system is used to provide the best combination of driveability, fuel economy, and emission control. In this system, short term fuel control is accomplished by the ECM rapidly responding to the oxygen sensor readings. These changes finely tune engine fueling. The long term fuel trim control is determined by the trends of the short term fuel trim. The ECM uses the long term fuel trim to make course adjustments to the engine fueling. Under normal driving conditions, except power enrichment mode, the ECM attempts to maintain a

14.7 to 1 air/fuel ratio. Fuel trim values of 0% are ideal. If the value is above 0%, this indicates the engine is running lean. Therefore the ECM commands more fuel to the system in attempt to maintain a 14.7 to 1 air/fuel ratio. If the value is below 0%, this indicates the engine is running rich. Therefore the ECM commands less fuel to the system in attempt to maintain a 14.7 to 1 air/fuel ratio. The ECM stores fuel trim values for three different speed/load ranges: idle, medium speed/load, and high speed/load. DTC P0171 will set if the long term fuel trim value exceeds a calibrated upper level in any of the above described speed/load ranges. DTC Parameters

DTC P0171 will set if the vehicle is in closed loop and the following fuel trim limits have been exceeded:

• Idle: 7.7%. * Medium engine speed/load: 21%. * High engine speed/load: 21%.

DTC P0171 diagnostic runs continuously once the above conditions have been met.

P0171 is a (type B) DTC. Diagnostic Aids

DTC P0171 indicates the engine is running lean. The following are possible causes of a lean air/fuel mixture:

• Vacuum leak. * Fuel pressure low. * Fuel quality poor or water in fuel. * Exhaust manifold gasket leak or leak around HO2S bank 1 sensor 1. * Fuel injectors clogged.

To verify the system is running lean, use Scan tool to monitor HO2S BANK

1 SENSOR 1 and HO2S BANK 1 SENSOR 2. If HO2S bank 1 sensor 1 lambda value is greater than 1.2 and HO2S bank 1 sensor 2 is below 300 mV, the system is running lean and the oxygen sensors are probably not at fault.

That was a GREAT description. Thank You. May I ask where you got that from? Similar information might be useful in the future. Oppie

I was still getting the P0171/P0174 codes. Pulled the MAF and sprayed down with cleaner. Checked fuel pressure which is holding at 49psi, reset the codes and hope for the best again. Plenty of torque at low speed but at high RPMs (3500 and up) the torque is not there. I've got to check the fuel pressure under load. Found that my old R12 air conditioning service gauge will fit the fuel pressure test port.

Noted that the TRAC light is a good precursor that the SES light is about to go on. Evidently, when there are engine management issues, the Traction Control system is shut down. This has been happening about 10 miles before the SES comes on.