Code Help

fast90lx · 05-02-2003, 10:06 AM

New to board.My mustang was running like a dog,so I pulled codes 81 KOEO and 41 and 91 KOER. The code reader manual says 81 is thermactor air diverter TAD solenoid circuit failure or electo-drivefan circuit failure or IAC Valve circuit failure.My Hanes manual says 81 is thermactor air circuit. It has relatively new IAC WTF. I would assume 41 nd 91 mean i need new o2 sensors 41 voltage low value lean 91 same. Hanes says 91 o2 sensor problem,fuel preasure out of range or injectors out of balance.I could use some advise on these codes

wrighr01 · 12-02-2003, 10:28 AM

Recently got the same error codes after experiencing engine surge/ bucking, backfiring symtoms. Ford Engine / Emission manual verifies by checking resistance through TAD solenoid (i had open circut). Believe the 41 and 91 codes (sensing lean mixture) are result of TAD valve in downstream position. Ford dealer wants $95 for this solenoid.:eek: Still looking for used (or cheaper) one.

Hethj7 · 12-03-2003, 03:05 PM

Code 91 means that your drivers side O2 sensor is reading lean. Since the right side is reading normal, that rules out a vacuum leak or a fuel pressure problem. Likely causes are a bad O2 sensor, or a bad injector in cylinders 5-8. If you don't have a miss, it's the O2 sensor. If you do have a miss, do a power balance test, and see which cylinder it is.

This is from PKRWUD, who really knows his stuff. When I had the 91, I replaced my o2 sensor and that cleared the code. Sorry, I don't know about the others.

Serach the site for posts about codes.....most of these have probably been covered at one time or another.

Hethj7 · 12-03-2003, 03:07 PM

Oh, keep in mind that I only had the code 91 as far as 02 sensors go. pkrwud said that was the driver side....I don't know what would show up if it was both side or just the passenger side.

05-02-2003, 10:06 AM	#1
fast90lx Registered Member Join Date: May 2003 Location: ohio Posts: 1	Code Help New to board.My mustang was running like a dog,so I pulled codes 81 KOEO and 41 and 91 KOER. The code reader manual says 81 is thermactor air diverter TAD solenoid circuit failure or electo-drivefan circuit failure or IAC Valve circuit failure.My Hanes manual says 81 is thermactor air circuit. It has relatively new IAC WTF. I would assume 41 nd 91 mean i need new o2 sensors 41 voltage low value lean 91 same. Hanes says 91 o2 sensor problem,fuel preasure out of range or injectors out of balance.I could use some advise on these codes

12-03-2003, 03:05 PM	#3
Hethj7 Mizzou Tigers Join Date: Apr 1999 Location: weston, MO United States Posts: 1,455	Code 91 means that your drivers side O2 sensor is reading lean. Since the right side is reading normal, that rules out a vacuum leak or a fuel pressure problem. Likely causes are a bad O2 sensor, or a bad injector in cylinders 5-8. If you don't have a miss, it's the O2 sensor. If you do have a miss, do a power balance test, and see which cylinder it is. This is from PKRWUD, who really knows his stuff. When I had the 91, I replaced my o2 sensor and that cleared the code. Sorry, I don't know about the others. Serach the site for posts about codes.....most of these have probably been covered at one time or another. __________________ 2006 Mustang GT 1990 LX GT-40 motor 262 horsepower, 307ft-lbs (sold but forever loved) 1998 Contour SVT Rice Haters Club Member #244

12-03-2003, 03:07 PM	#4
Hethj7 Mizzou Tigers Join Date: Apr 1999 Location: weston, MO United States Posts: 1,455	Oh, keep in mind that I only had the code 91 as far as 02 sensors go. pkrwud said that was the driver side....I don't know what would show up if it was both side or just the passenger side. __________________ 2006 Mustang GT 1990 LX GT-40 motor 262 horsepower, 307ft-lbs (sold but forever loved) 1998 Contour SVT Rice Haters Club Member #244

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12-02-2003, 10:28 AM	#2
wrighr01 Registered Member Join Date: Dec 2003 Location: New Jersey Posts: 1	Recently got the same error codes after experiencing engine surge/ bucking, backfiring symtoms. Ford Engine / Emission manual verifies by checking resistance through TAD solenoid (i had open circut). Believe the 41 and 91 codes (sensing lean mixture) are result of TAD valve in downstream position. Ford dealer wants $95 for this solenoid.:eek: Still looking for used (or cheaper) one.