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Lack of O2 switches, Mercury Mystique

Sent to Car Experts June 13, 2006 11:15 a.m.

I have a 1999 Mercury Mystique, 2.5 engine, 116,000 miles, auto transmission. Trouble codes: 1131 and 1151, Lack of HO2S-21 switch indicates lean. Please explain this problem in lay terms. What are some situations that can cause this and the possible remedies. What are some trouble shootings that I can do to remedy this problem? Car runs great, gets great gas mileage. If the check engine wasn't on. I couldn't tell if there was a problem. Any suggestions appreciated.

Optional Information:
1999 Mercury Mystique 2.5

Already Tried:
Nary a thing

Customer (name blocked for privacy)

Status: Closed Value: $15

Answer
June 13, 2006 9:48 p.m. (10 hours and 32 minutes later)

ACCEPTED

Those codes mean that the O/2 sensors are reporting a constant lean condition and the computer has already compensated for this to it's limits.

The most common cause for this, especially in a Ford is a sever vacuum leak. A common problem with these is deterioration of the rubber vacuum hoses or the connecters for them at the manifold. With the engine idling, listen closely for a hissing noise and try to follow it to it's source.

What you may find is a hole being sucked open when the engine is running but closing over when shut off.

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Reply
Sent June 15, 2006 9:33 a.m. (1 day and 11 hours later)

Relist: I still need help.
Electronic stethoscope could not detect vacuum leak either from vacuum hoses or intake. What would you check next? I don't want to change the o2 sensors if there is no need to.

Customer (name blocked for privacy)

Answer
June 15, 2006 10:16 a.m. (43 minutes and 12 seconds later)

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Hammer Time -- L1 Master Technician -- 98% Positive Feedback on 2710 Car Accepts
ASE Mastertech with Adv level Engine performance cert.

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