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Zetec Upstream O2 Sensor Replacement

S

Scorpion8

Hard-core CEG'er
Joined
Jul 10, 2008
Messages
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Juneau, AK
I got in a replacement O2 Sensor for the upstream position on my Zetec engine. This is to eliminate a check engine light PO135 code that stays on. There's a nice PDF availavble on the V-6's on changing the O2 sensor, but I don't see one for the Zetec because.... man, looking at where that's located, that's gonna be hard to get at. I don't see a lot of stuff that can be removed to get in there easier.

Any tricks before I begin? Helpful hints? Where does someone get the O2 sensor socket shown in the V-6 help file? That definitely looks like it would help, or else a crow's foot open end or box end wrench on the end of a looooong extension bar.

Any experienced help would be appreciated. Thanks.
 
the O2 sensor socket and a rachet or wrench is all thats needed. its actually really easy, so much easier than the V6 (I just did both uppers on my SVT it sucked). I changed the one in the zetec in autozones parking lot once.

the O2 sensor socket can be bought at any auto parts store (or rented for that matter) or Sears
 
Thanks. We have Napa, PartsPlus and a brand new Schucks (been open for 3 days). I hope one of them has the socket.
 
Schucks had the proper O2 sensor socket. Took about all of 10 minutes to fix. Problem cured, and check engine light cleared. Thanks!
 
Replaced, and the problem doesn't clear. I can clear the CEL but a short while later it comes back. No set time or distance, it varies each time. Usually on the 2nd time I turn the key.
 
is the upstream one located on the exhaust manifold below the dipstick?

:shrug:
 
Scorpion8 my 98 zetec threw an different code for upstream 02 sensor, p1139 or something like that. Search the forums for an OBDII code list, I know Tony 2005 has posted it a few times. I think you may have a different issue... XF
 
That P0135 code is the only one I get, and I can clear it but it always comes back the 2nd time I operate the engine after clearing it. There must be an intermittent ground somewhere that's causing it.
 
[FONT=arial,verdana,helvetica,sans-serif]P0135[/FONT][FONT=arial,verdana,helvetica,sans-serif]Upstream Heated Oxygen Sensor Heater circuit fault - Bank No. 1. [/FONT]


check the fuse for the O2 sensor heater circuit
 
power box under the hood .... shouldn't be a surprise, that is what the code says. so the starting point would be to check the fuse.



note you may have to replace that new sensor again as it isn't good to run a heated O2 sensor that doesn't have the heater working correctly.
 
Fuse 13, 20A says "HEGO Sensor" which I took to be "Heated Exhaust Gas Oxygen" sensor. It was fine and un-popped. I worked it in and out a couple of times to renew the contact and re-set the PCM using my code reader. We'll see on the way home, but am doubtful that's it.
 
That code has two trip detection logic. Meaning, the first time the car is run, the code is set as "pending" and the second as "current" which sets the light. The fault is always there. You will need to ohm out the wires between the upstream 02 sensor and the ECU. If you replaced the sensor and the code persists you likely have a wiring problem. Our wiring harnesses (especially on the first 3 or 4 production years) are known for deteriorating. Get yourself a DVOM and a good wiring diagram that shows ECU connector pinouts.
 
NOW THERE'S THE ANSWER I'VE BEEN LOOKING FOR, FINALLY!!!

Thank you. It is always the 2nd time I key it. I reset it at lunch, and I drove it home and stopped halfway, and it was fine (no CEL). Came on the 2nd time I keyed her over. I reset it,and it did it again. I'll gather my stuff (have plenty of meters) and follow this wiring harness from A to B.

Can I just buy a 4-wire stand and run entirely new wire from the sensor to the ECM?
 
Of the 4 wires, the WH (white) goes straight to the PCM. The VT/YE (violet/yellow) goes the fuse box to Fuse 13, so that's probably a power fuse for the heater circuit - the fuse is good so it's not grounding and blowing. The BK/YE (black/yellow) goes to a junction which is a combined ground, so excess ground there shouldn't be a problem if there's a short. Finally the BN (brown) goes to a junction with the legs of 2 other sensors (Intake Air Temp, another and also combines with other multiple junctions from many other sensors).

If I was a betting man, I think I'll work on the WH (white) wire first since there isn't any PCM codes from any other sensors in any of those combined junctions.

Sound okay?
 
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