2001 Boxter S P0102, P1126 and P1133

I bought a 2001 Boxter S and the Engine light is on. The code is P0102,P1126 and P1133 and says Mass or Volume Air Flow Circuit Low Input. A mechanic took the light off and after 150 km came back again.If I replace the MAF sensor would rectifie the problem?
Thank you.

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[Nick at Pelican Parts]

The MAF could be the issue. However, you'll want to check the fuel trim data to see when the vehicle is out of spec. This data will help you diagnose the MAF or any other component that could be setting the fault codes.

- Nick

[thom4782]

If you haven't done this already, perhaps the first thing to do is to clean the MAF and see if the problem goes away.

[paulv]

I would go with thom4782's advice (clean the MAF) as P1126/1133 are fuel adaptation codes specifically for the lower load range (not idle or upper load range). Consequently, your LTFTs would be normal at the other ranges and out of whack for the lower range. This is what Nick was talking about and is a professional troubleshooting technique to prove that the MAF has failed, but you would need a Durametric or Global OBD2 scanner to see this data. The P0102 is specifically for the MAF (open circuit, short to ground, or just the MAF is defective). The P0102 is most likely causing the other codes to be set. A good scanner would tell which code actually set the CEL.

Buy a can of MAF cleaner (don't use anything else) and try cleaning it first. Don't reset the code, let it reset itself after all the internal tests are performed.

Regards,
paul...

[ELoomis]

I agree you should not reset the codes but it will take three complete error free drive cycles for the system to turn off the CEL. The Bentley defines a drive cycle as a cold start and run up to at least 160 degrees F or 40 degrees F above its starting temp. Good luck.

[rskovira]

Paulv- What values would you log with Durametric software to determine if the MAF is causing the P1126 and P1133 codes?

[paulv]

Originally Posted by rskovira

Paulv- What values would you log with Durametric software to determine if the MAF is causing the P1126 and P1133 codes?

It would be better to measure the voltage of the MAF with ignition on (engine not running) and then with the engine at idle. For the Alex's MY, those values would be 0.9-1.1Vdc, and ~1.4vdc, respectively. You will need a wiring diagram to identify pins.

For the long term fuel trim values, Durametric calls them (for my '07, DME 7.8_40), "Fuel Trim Adaptation xxxxxx": RKAT (near idle), FRAU (lower load range), and FRAO (upper load range) -- these are available on both banks. As Nick mentioned, you will need to check across the range to see when the fuel trims go out of spec.

Regards,
paul...

[rskovira]

At engine not running I get 0.9-1.1 V and at idle I get 1.29-1.3V. Is 1.3 okay?
I'm running Durametric version 6.3.1.7. It has RKAT for long term and FRA for short term adaption for both banks. None of the adaptions change at all when I go out for a run and do data logging. RKATs are solid at -1.13 and FRA stays at 1.30%. What is an out of spec condition for fuel trim, 10%?

[paulv]

Originally Posted by rskovira

At engine not running I get 0.9-1.1 V and at idle I get 1.29-1.3V. Is 1.3 okay?
I'm running Durametric version 6.3.1.7. It has RKAT for long term and FRA for short term adaption for both banks. None of the adaptions change at all when I go out for a run and do data logging. RKATs are solid at -1.13 and FRA stays at 1.30%. What is an out of spec condition for fuel trim, 10%?

Don't know what the out of spec values are, but what you're reading are within the nominal values (depending on DME version, 7.8 has FRA at ~1.03 +/- 0.04). On other cars I've worked on, LTFT ranges +/- 20% which will cause the CEL. Preferably, LTFTs should be +/- 5% and no more than +/- 10%. When they are beyond the +/- 5%, the engine should be investigated for impending problems, and really investigated when they're more than +/-10%. BTW, the newer, DFI engines have LTFT ranges of +/- 25%. HTH.

Regards,
paul...

[rskovira]

Yes that gives me an idea of the magnitude. I cleaned the MAF again and got 85 miles instead of 45 miles until the CEL came on again with same codes 1126, 1133. After data logging LTFT, STFT and O2 I don't see any thing I think should be throwing the CEL. However and what I need help understanding is why my LTFT is negative 1.83 and my STFT is positive 1.31????? Other car forums blame this on a bad MAF. Why would a bad MAF cause this condition??

75k miles original MAF (I think)
2000 Boxster S

[rskovira]

Maybe my confusion is I thought FRA is short term trim and RKAT is long term trim. Now I'm thinking I' wrong and both are long term trin but RKAT is at idle and FRA is at lower and upper load. Is there a short term trim variable?

[paulv]

Originally Posted by rskovira

Maybe my confusion is I thought FRA is short term trim and RKAT is long term trim. Now I'm thinking I' wrong and both are long term trin but RKAT is at idle and FRA is at lower and upper load. Is there a short term trim variable?

I haven't seen any (again, for my '07) equivalent STFT values on Durametric. Did you look (or is it possible?) to check/graph the upstream O2 sensor on your car? This would tell you how far off you are.

Regards,
paul...

[rskovira]

My O2 sensors oscillate between .1 and .8 and appear to be working.

Again error code is P1126 and P1133.

FRA +1.29 and RKAT -0.89

Why is one positive and the other negative?

Will these values throw the CEL?

2000 Boxster S with 75k miles

[rskovira]

After 125 miles FRA is +1.31 and RKAT is -2.25. Looking for inputs as to what would cause the RKAT to swing negative???

[paulv]

Originally Posted by rskovira

........................ Why would a bad MAF cause this condition??

.................

Because it would incorrectly measure the air coming in and reporting that incorrect value to the DME which would then adjust the mixture but the O2 sensor would report something different back to the DME, and so on and so forth..... equals CEL.

Regards,
paul...

[paulv]

Since P1126/1133 are set because the mixture is so lean the adaptation is pegging it rich to compensate.

Sent you a PM.

Regards,
paul...

[MarkRobinson]

so what was the outcome of this issue? My '01-S just gave me the same codes...on light throttle it toggles back between 5 & 6 cylinders it feels.

Mark