CEL, Fuel trim code and Readiness failed help needed ...

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Apr 1, 2006 | 01:46 PM

N9909E

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CEL, Fuel trim code and Readiness failed help needed ...

<center><img src="http://pictureposter.audiworld.com/51787/readiness.jpg"></center><p>Got the "Fuel trim" code and replaced MAF w/refurb, next day got same code and Readiness failure:

17544 - Fuel Trim: Bank 1 (Add): System too Lean
P1136 - 35-00 - -
Readiness: 0110 0101

Group 032 indicates 7.1% at idle and g/s is around 178 top end, so I am confused. It doesn't look like MAF. Could bad O2Sensors be causing all this?
Thanks

Apr 1, 2006 | 02:44 PM

~~Uwe@Ross-Tech.com~~

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Check intake for leaks.

The strange thing is 7.1% should not be enough to set a code. Did you clear codes recently?

Clearing codes will also set your readiness bits to fail.

-Uwe-

Apr 1, 2006 | 07:41 PM

N9909E

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Yes, cleared codes and each time CEL comes back w/ Fuel Trim

Isn't that Catch-22 - clearing the codes sets the Readiness to fail?
Thanks

Apr 2, 2006 | 05:44 AM

~~Uwe@Ross-Tech.com~~

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It was designed that way quite intentionally

by the bureaucrats who wrote the OBD-II specs so a car can't have a clean bill of health simply by clearing codes. A "clean bill of health" (no DTCs and all readiness bits reading pass comes only after the ECU has had the opportunity (or been forced to) run all the tests of the emissions related systems. When each of those tests is run, the relevant readiness bit will either get set to "pass" or a new DTC will be set.

-Uwe-

Apr 2, 2006 | 09:17 AM

N9909E

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Log inside - I really don't see any cause of lean condition -

<center><img src="http://pictureposter.audiworld.com/51787/log_040206.jpg"></center><p>I don't have a DTC for failed O2 Sensors, so if I find out what's the cause of leaness (or maybe this replacement MAF is bad?) the Readiness check w/eventually pass all?
Made a run and logged 002, 032 and 115 - all look good to me.
Air mass is down from 175 g/s to about 155 I assume cause it's 80+ deg. today.
Thanks much,

Apr 2, 2006 | 03:01 PM

~~Uwe@Ross-Tech.com~~

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I don't think it's the MAF.

They tend to throw the second fuel trim group (part throttle) not idle. What tends to throw the first group is a small leak in the intake system past the MAF.

Readiness will eventually pass by itself (or throw another code) or you can force it (13-step procedure in Bentley).

-Uwe-