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0 voltage reading on both O2 sensors

(2001 Ford Escort)
in Round Rock, TX on June 26, 2011
Have 2001 Ford Escort 4 door sedan. The check engine light was on, hooked up car OBD II to laptop using Autotap program for reading codes and real-time sensor outputs. Both O2 sensors read 0 MV. Replaced both O2 sensors with new Bosch units and cleared fault codes with program. Both new O2 sensors still read 0 MV. Changed out front sensor with another new Bosch unit and both still read 0 voltage. Tried new computer and still no sensor voltage. Rang out harness wiring and found no opens. Can't get car to complete emissions check without O2 sensor reading to pass state inspection. Car runs great
Displaying 2 answers & 6 comments
Popular Answer
on June 26, 2011
What codes are coming up?
on June 27, 2011
When one comes up it's P0171. This is my God daughter's car who lives next door. We took it to the Ford dealer and they said the injector o-rings were leaking. The cost of replacement was $685, I did it for $6.50 of o-rings and a $8.00 large pizza. I sprayed the engine with carb cleaner while running and got no RPM change. Cleaned the EGR valve, replaced fuel filter, just can't find any reason for lean code
on June 27, 2011
$8.00 pizza, I like that...

Have you checked the MAF sensor and the air tube? The MAF is very capable of throwing lean codes. Check the BARO reading - it could be that your car is thinking you are at 20,000 feet, and is dialing back your fuel accordingly, causing a lean code.

on June 28, 2011
First off, I do thank you for the replies, Wrench Master. I did clean the sensor wire on the MAF with Elctro-Contact cleaner. Though the tube itself is leaving my hands black with rubber, I didn't see any cracks or breaks in the tube. I also cleaned the throttle body. I drove it yesterday for about 50 miles to try to complete the drive cycle for the emissions check. The Autotap program will show when the 8 checks are complete. 6 of the checks are complete, with the evaportive system and catalyst system still showing as incomplete. After about 45 miles the P0171 code showed up again. The check engine light has not come back on yet, but it will. What's really bugging me is the O2 sensor readings. Even though in the emissions check, the program is showing a green COMPLETE for O2 sensors and O2 sensor heaters, the real-time readings screen is showing 0 MV for both O2 sensors. I did plug the laptop into my God daughter's mom's car, 2003 Ford Focus, and I am getting an active reading on both O2 sensors, so I know that part of Autotap is working. Still not sure if there is a connection with that situation. I am tempted to just replace the intake manifold gasket, but at 115,000 miles, that shouldn't be a problem. Besides, I did spray the gasket area with carb cleaner and got no change in engine RPM. I'm using Alldata on-line maintenance manual for reference and don't see any voltage or resistance checks for the MAF. I have had problems with Ford/Mercury MAFs in the past, but cleaning them has always corrected the problem. You could be on to something there, but at $100 for a reman at Autozone, I hate to just throw parts at the car (shot gunning) in the hope one may fix the problem. I would like to check the MAF if I can get the correct numbers to look for. Getting ready to go look the engine over, one more time, to make sure I haven't missed something obvious, like a cracked vacuum nipple. Thank you again for the come backs!
on June 28, 2011
So - here's the thing - never shotgun the parts, especially with your handy-dandy Autotap deal.

Look for the BARO reading, or even the MAF reading in voltage - 1.59 volts would be equivalent to sea level, 1.56v is 1000 feet, 1.53 is 2000 feet, etc...

If the voltage is really much lower, then this reading could be out of line, causing the lean code.

I'm with you on the O2 readings though - you should have something. If you have nothing, it's possible the system is not going into closed loop? Can you check that parameter? This could be due to the engine not getting to proper operating temperature for example.

Or, check for an open wire in that harness...possible also.

Good luck...
on July 03, 2011
Hello Wrench Master, just wanted to fill you in on the latest. Discussed issues with my God daughter's Dad and he said to go ahead and replace MAF. Did that and did the drive cycle with him. The P0171 code popped up again, but this time Autotap showed it had passed emissions test and there was no check engine light illuminated on the car. I finally threw up my hands and said "WTF", told her Dad to go ahead and take it down to the inspection station, it will either pass or won't. He took it down and they said everything checked out good, including the O2 sensors. But, as soon as they hooked it up to the testing computer, the check engine light came on and showed the P0171 code. It failed inspection. Now, bare with me Wrench Master, it gets better. They told him their shop's computer would tell them exactly what was wrong, all the way down to a loose wire. Once again I said "WTF, go for it, I'm out of suggestions." So, they hooked it up and said the downstream O2 sensor was bad (which they said was good on the state inspection computer) and there was 2 bad vacuum hoses. Said they fixed it and slapped an inspection sticker on the car. $225.00. I was sort of happy, but at least the car is now inspected. I talked Dad into sending back the reman computer and eating the restocking fee, to offset some of the $225.00 repair cost. He agreed. I was moving the car to my house next door and when I started it, the check engine light popped on, again. I popped the hood and looked for the new vacuum hoses and couldn't find them. The O2 sensor was replaced when I first started this, so I don't think it was bad. I know the dealers computer can make a car show it has completed a drive cycle without actually driving the car, so I'm guessing their's can too. I really feel they did what the dealer was going to do with the $685.00 injector o-ring change. Throw some parts at it, complete the drive cycle with the computer and slap an inspection sticker on the car. Then when the light comes back on, they say, well now you need this too. After 30 years in aircraft maintenance, I thought it was too good to be true and can't accept when a problem isn't "really" fixed. So Mr. Wrench Master, we're back where we started, but now have a year to figure it out. Sorry for the long winded reply, but it comes from making aircraft maintenance log entries. Thank you for your suggestions and help. Take care
on March 07, 2013
check the voltage at the sensor for true voltage.Possible open circuit or fuse blown.the down stream sensor wiring can short on heat shield ive seen several do check voltage ,use straight pins and push into the wires at about a 45 degre angle about an inch apart so they cant touch each other. when you are through you can remove the pins and rub the spot where they are inserted to seal the opening.
on July 03, 2013
have a 98 mercury mountaineer with same problem; had p171 and p174 showing lean burn both banks; turned out to be lower intake manifold gasket for the p 174 ( bank 2 )apparently; now still have p171 bank 1 too lean. replaced : maf / fuel vapor management valve / fuel pump - new style; factory fuel pressure regulator was removed; i think new pump has one built in ??. / dpfe / solenoid that controls dpfe / pcv valve / egr valve / tps /both upstream O 2 sensors / fuel filter. car runs smooth but with lack of power at higher speeds. did not replace catalytic converter or down stream o2 sensors ,injectors, spark plugs or ignition electronics yet. fuel and ignition show ok on diagnostics. catalytic always shows inconclusive. i am thinking maybe a bad cat that wont get up to operating temperature. smoke test always has checked good except for some very minor leakage on idle air control valve ; has been fixed ; no difference. computer was bad in respects to controlling transmiision shifting; changed computer for that problem with no noticable difference to p171 code coming up; in case computer had a problem there which it didn't.
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