Code P0170, 98 CL600. Have freeze frame data
 

1998 CL600, 84,000 miles owned since April. Friday the CEL came on with P0170 - Fuel Trim (Bank 1). At the time I had only a simple OBD2 reader. I cleared the code and the CEL remained off. On Sunday I purchased a better OBD2 scanner that can read live data. Sunday evening I noticed that I have a pending P0170 code. This morning I swapped the two MAF sensors thinking if one of them was the problem the code would switch to Bank 2. Today at lunch the CEL came on again with P0170. The scanner read the following freeze frame. I also captured some live data after the light came on. The car is running very smooth at idle and strong during acceleration. Two things that I'm concerned with are the engine temperature (212F) and the manifold pressue (12.9 inMg). Shouldn't the vacuum be higher? Most cars I've had before are at 18-20. Tonight I'll attach a vacuum gauge. The car is running very smooth so I'd be surprised it had a vacuum leak.


Freeze Frame Data

Fuel Sys 1 CL
Fuel Sys 2 CL
Calc Load(%) 16.8
ECT(F) 212
STFT B1(%) 3.9
LTFT B1(%) 0
STFT B2(%) 0
LTFT B2(%) 1.5
MAP (inHg) 12.9
Eng RPM 525
Veh Speed(mph) 0

Sample Frame of Live Data (after CEL came on)

Fuel Sys 1 CL
Fuel Sys 2 CL
Calc Load(%) 19.2
ECT(F) 212
STFT B1(%) -6.2
LTFT B1(%) 2.3
STFT B2(%) 0
LTFT B2(%) 0
MAP (inHg) 15.6
Eng RPM 1173
Veh Speed(mph) 9
Spark Adv -19
IAT (F) 105
MAF (lb/min) 3.026
TPS(%) 6.6
Air Status OFF
O2S B1 S1 (V) 0.780
STFT B1 S1(%) -3.1
O2S B1 S2 (V) 0.685
STFT B1 S2 (%) NA
O2S B2 S1(V) 0
STFT B2 S1(%) 0
O2S B2 S2 (V) 0.770
STFT B2 S2 (%) NA

No LTFT on B1?

This data is really useless to address the issue at hand. The code you set is for exceeding the adaptation capability for a range of operation. I don't remeber whether it is CTP (closed throttle position) or part load. I also don't remember whether your fuel system has just part load or has lower partial and upper partial. If it has upper and lower then there are three ranges that could be faulted. Using only LTFT you can not view any of them. It is some arbitrary average.

The data shows almost no Long term fuel correction on bank 2 and is not showing bank 1 at all. Seeing MAF in lb/min is really goofy, but really wouldn't tell us much anyway as the car is obviously not at idle but barely pulling off. The only hint of an issue is the STFT at -6.2, but STFT doesn't set codes and that is well within accepted range anyway.

Thanks for replying. There was a typo in my original post. I do have values for LTFT B1. I've corrected the original post. I'm using an Innova 3130 scanner. I can changes the units. Would you rather see everything in metric? I've watched the LTFT B1 with the scanner in live mode. The highest I've seen is +2.3. My understanding is it would have to be much higher than that to trigger a code. Is the dealer able to read more data than I'm able to with the scanner? I usually take the DIY approach first but if I don't have the equipment I'm willing to take the car in.

So far I've noticed that the code always occurs at idle (car speed 0). Today I just got a code when I parked at my garage door. Unfortunetly the reader lost the data somehow. I'm starting to suspect maybe I do have a vacuum leak. I feel a slight lope at idle that I didn't feel last week. Also, I put a bottle of Techron into the tank last week.

I've spent a few days unsuccessfully trying to capture live OBDII data when a DTC error occurs. What I've observed is that when I do get a code the scanner doesn't see it until the ignition is shut off and back on again. So either (a) the condition for the code is occuring when the engine shuts off or (b) the ECU on this car doesn't report DTC events during live data mode. I'm suspecting (b) is the case. Can anyone confirm this?

I'm still getting P0170 but not every time I drive the car. I looked for vacuum leaks and sprayed some starter fluid around the injectors. I didn't find any problems. Since M120 has two of everything I'm going to switch things left-right to see if I can get a code P0173 (Fuel Trim Bank 2). I've already switched the MAF and intake temperature sensors. Tonight I'll switch the O2 sensors.

Any other suggestions are welcome. Thanks.
-Dave

Do you have adaptation for idle? Should be something like CTP...
I had a similar problem with older LH system. The car would set fuel trim code and only CTP adaptation was out of range. I found vacuum leak at the cracked EGR pipe. The leak was only big enough to cause trouble with CTP adaptation. As throttle was opened, the percentage of the leak was to small compare to the normal air flow to cause partial or full throttle problem.
Your car doesn't have EGRs, but check rubber intakes between MAF and throttle actuators for leaks. Driver side would be a primary concern as it has to be disturbed during oil changes.
Mike

I don't think the adaptation value is available from an ODBII scanner. I'm starting to understand that only a MB scanner can read this and other important information. Unless I find something obvious wrong in the next few days I'll take the car to the dealer for analaysis. Thanks for responding.
-Dave

I believe the trims are the same as adaptation. I don't believe there is any other engine data that another scanner can read.

Remember that the "A" in MAP is for Absolute. The 18-20 you are remembering is gauge pressure (vacuum). As I recall they are basically opposite. At WOT you will have a very low gauge vacuum and a very high MAP pressure. At idle you will have a high gauge vacuum and a low MAP pressure.

Well you are wrong. P0170 is a code for exceeding the adaptation range. The way you diagnose it is to view the various adaptations and see which one is out or close. OBD data is a very rough approximation and from the stated values here it is obviously useless in this case. The adaptation values exceeded take considerable time to change. The numbers when looked at properly are easy to deal with.

On Monday I replaced all four O2 sensors and the fuel filter. Since then no codes. The car idles so smooth you need to look at the RPM guage to confirm the engine is running (or just step on the go-fast pedal :evilgrin:).