O2 sensor | Ford Explorer Forums - Serious Explorations

  • Register Today It's free!

O2 sensor


September 6, 1999
Reaction score
Help Guys,

Last week my 91' Explorer's check engine light came on. Used the code scanner and it showed a lean O2 sensor reading. I replaced the sensor and now a whole new set of problems,, The transmission don't want to shift from 1st gear until about 4,000 rpm's and the check engine light come on intermitently,, comes on for about fifty miles then goes back off... Tried reseting the computer and it is still the same. So if any of you guys might know what's going on please help.

Join the Elite Explorers for $20 each year.
Elite Explorer members see no advertisements, no banner ads, no double underlined links,.
Add an avatar, upload photo attachments, and more!

Well guys, I fixed the trany problem. I knocked off a vacuum line putting on the new O2 Sensor. However the check engine light still continues to come on. The stored computer code is Code 41, with the engine running the code is code 42. I have cleaned the MAF and reset the computer with no help. The light is coming on about 5 to 7 minutes into trip. You can switch of engine and it will go off but come back on at about the same time interval. I haven't changed the plugs and wires yet, Any ideas?

[This message has been edited by jmarley (edited 09-08-1999).]

Hey jmarley,

did you ever get your check engine light to go off?? mine started coming on this weekend but its not running any different.
I used the code scanner and got a 73 (insufficient throttle position change) this time. Any suggestions from anyone is welcome

Some days you get to be the Statue,
Some days you get to be the Pigeon!!

The stored code you are getting 41 is a code for the O2 sensor that is not switching state. Now the the running code 42 is for a rich running engine, not lean. What I would have checked is the fuel pressure. The fuel pressure regulator might be sticking and causing excessive fuel pressure. I just had that problem on my '91 explorer. The regulator on my truck was intermittently sticking and I was getting a code 42 and when I checked the fuel pressure it was reading not 35psi which is normal,but, around 70 psi. I replaced the regulator and the problem was history.

[This message has been edited by slow-demon (edited 10-28-1999).]

Where do you guys get these scanners and are they very expensive also do they have a book that tells you what the codes mean

Hey Ryan,

You can get the code scanners at any of the parts houses, and they cost in the neighborhood of $30.

To my knowledge they do not have a scanner available yet for the EECV, but the EECIV scanners do come with a book explaining the codes.

I don't know what year truck you have, but be sure to check to see if its an EECV or EECIV. I don't know off hand what year they switched, but its pretty easy to spot. An EECV computer car has a tag on the firewall on the passenger side of the truck.

Good luck, Rob

no Explorers, but plenty of Fords:
'82 Mustang GT 351W
'82 F250 351W
'91 Mustang LX 5.0
'78 Mustang II pro street


I have a 94 explorer auto trany 4.0
What Exactally is EECV and EECIV

EECIV & EECV stand for Electronic Engine Control 4 & Electronic Engine Control 5
A '94 has the EECIV.

thanks for the info guys, I have fixed the problem. It was the fuel pressure regulator, my pressure was running around 90 psi. Fuel mileage was around 10 mpg before I changed the regulator and now it's 17. Thanks again guys for all the help.