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'92 Sc400 Engine Code 25

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Engine Code 25, Air-Fuel Ratio Lean Malfunction.

Any speculation on the probable cause of this and/or how to repair?

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How well does the car run? I'll check the diagnostics when I get home. You're lean. Means not enough fuel. Could be anything in that area. I'll check the code.

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(1). Main heated oxygen sensor voltage is .45v or less (lean) for 90 sec. under conditions (a) and (b ).

(2 trip detection logic)*

(a) Engine coolant temp. 60 C (140 F) or more.

(b ) Engine speed : 1,500 rpm or more

Trouble area:

Open or short in main heated oxygen sensor circuit

Main heated oxygen sensor failure

Ignition system

Engine coolant temp. sensor

(2). Main heat oxygen sensor voltage is alternating above and below .45v at 5 times / sec. or more under conditions (a) and (B).

(2 trip detection logic)*

(a) engine speed: Idling

(b ) engine coolant temp : Between 60 C and 95 C (140F to 203F)

Trouble area:

Open or short in injector circuit

Fuel line pressure (injector blockage)

Volume air flow meter (air intake)

Engine ground bolt loose

Foreign object in valve

(3) Difference of air fuel ratio feedback compensation value between right and left banks is more than 10% for 30 sec or more under conditions (a) and (B).

(2 trip detection logic)*

(a) Engine speed : 2,000 rpm or more

(b ) Engine coolant temp : between 60 and 95 C

Trouble area:

Fuel line pressure (injector leak, blockage)

Mechanical system malfunction (skipping teeth on timing belt)

Ignition system

So there you have it. One or all of these issues - pretty much all related. When was your last tune up? Get a full tune up if you have not before. Change the timing belt if it has not been done. Replace all o^2 sensors and go from there. The factory service manuals are worth their weight in gold.

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Car runs well, no other noticable symptoms. It does sit quite a lot now as Sandra drives her Miata on the cool sunny days. It was borderline on its last emissions test (I forget which test).

Thanks for the invaluable advice!!

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david_meusa Writes:

"Hi, 92 LS400, same problem. Did you fix that problem?"

Dave:

I would image. Are you experiencing the same problem?

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david_meusa Writes:

"Hi, 92 LS400, same problem. Did you fix that problem?"

Dave:

I would image. Are you experiencing the same problem?

Can't find big difference, 155K miles on it. I reset the code, after abt 15 miles, check engine light comes again. Looks like it is heat related? I used some fuel cleaner today to see what happen.

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I have a feeling it might be 02 sensor related, when's the last time, if ever, you've replaced them?

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Engine Code 25, Air-Fuel Ratio Lean Malfunction.

Any speculation on the probable cause of this and/or how to repair?

I have a 91' LS400, recently I also got DTC 25 error code. My smog check failed with NO too high. Have you solved your problem ? What's the solution ?

By the way, here are my smog check numbers:

15 MPH: CO2 14.7%, O2 0.3%, HC 10ppm, CO 0.00%, NO 1119 ppm

25 MPH: CO2 14.8%, O2 0.1%, HC 7ppm, CO 0.00%, NO 769 ppm

Thanks

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Same problem here. I checked the main Ox sensors and the heating elements seem to be OK. I have changed plugs and fuel filter, no luck yet. I plan on wires and caps & rotors next. (Ifigure bit probably needs it anyway. Then, I guess I will pull the injectors for cleaning. Tried injector cleaner w/o sucess.

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