O2 Sensors

Roebuck Mazda sells the O2's for $147.64 4Feb99

Symptom

The most common cause of a Check Engine Light (CEL) is bad O2 (Oxygen) sensors. You can change these yourself, but read the below for important hints. Check the Probe FAQ on this site for how to read the computer codes yourself (1993-1995 only). Refer to the official Ford service manual for detailed installation instructions.

A bad O2 sensor will result in a rich mixture, lowering mileage and possibly performance.

Codes

Check the Probe FAQ on this site for how to read the computer codes yourself (1993 to 1995 only).

24 - Rear Oxygen Sensor

Where is It?

Front Sensor: Do you have an aftermarket intake? If no remove the first intake piece(where the air goes in first) which is right above the radiator. Then if you look between the engine and the radiator, you will see an exhaust pipe coming out of the engine. On that exhaust pipe you will see something that looks like a sparkplug with wires coming out of the top - that is your O2 sensor.

Rear Sensor: From bottom rear of engine it visible on the exhaust pipe. (Don't burn yourself if hot!) Apparently very easy to change.

3 Wire or 4 Wire

There is some confusion about which cars have the 3 and which have the 4 wire O2 sensors. It might be best to look at your car until we have this completely figured out.

California 93 PGT: 4 wire front O2 sensor (2 white, 1 black and 1 gray)

California 94 PGT: Front O2 sensor. Bosch 15709 as the replacement. This is indeed a 3-wire sensor. It fits perfectly. Plug is the same like OEM. The OEM sensor has a lot slimmer body than the Bosch. No CEL, so I guess it works fine. On another note, everybody who wants to replace the O2 sensor, do yourself a favor and get an O2 sensor socket. Seriously, I cannot imagine how would you replace the sensor without it, especially since the front sensor goes though the heatshield, so with no socket, you probably would have to remove the heatshield first, creating a big P.I.T.A. for yourself. By the way, the heatshield caused a little problem for me, because my installed sensor does not sit exactly in the middle of the hole on it, and so the O2 sensor socket would not go onto the sensor until I bent the heatshield a little, forcing the socket in... but then everything went just fine.

Bosch: They said 93-95 should have 4 wire- standard and 3 wire-CA but everyone on the list has got 4 wire sensors even in CA vehicles. Weird! They said 96-97 use 4 different 4 wire sensors but Howard checked it out on his Pgt and he has 2x4wire & 2x3wire. Even more wierd!

Part Numbers: Bosch #15708 (non California, 4-wire) & 15709 (california vehicle, 3-wire) These sensors are a direct replacement with connectors. to check which ones you need count the number of wires on your O2 sensrs and verify that you have a square looking connector. $64 each + $3 shipping on Dec98 bulk buy (Performance List)

NGK O2 sensors. They were back ordered for the longest time. They're direct fit and look exactly like the OEMs. For those who asked, the part number is 22028. It's actually badged as NGK-NTK. May99

Miscellaneous Ramblings

8Mar00: Here is the company that I ordered my O2 Sensors through. The prices below are for OEM style sensors with original connectors. The sensors I purchased did not come with OEM connectors so I had to splice them onto the original connector. They work perfectly and are stamped with the "ford" symbol which leads me to believe they are OEM quality. I paid $39.00 a piece plus $10 bucks shipping. Installation is a breeze and with Gas running upwards of $2 bucks a gallon, every little MPG counts. Here you go.

B & B Auto parts IN NEW YORK CITY. WE ARE A COMPLETE AUTOMOTIVE WAREHOUSE DISTRIBUTER.HERE ARE THE PARTS YOU REQUESTED: NEW BOSCH SENSOR 69.00 NEW AFTERMARKET 59.00 WE ACCEPT ALL MAJOR CREDIT CARDS AND SHIP MOST ORDERS UPS SAME DAY. YOU CAN EMAIL OR CALL US AT THE FOLLOWING NUMBERS USA TOLL FREE 1-800-475-1227 PARTS HOT LINE 1-718-597-4000 MON-FRI 9AM-6PM SAT 9AM-3PM EST. OPEN SATURDAYS 9-3 ALL PRICES DO NOT INCLUDE SHIPPING AS WE SHIPUPS,DHL,OR FEDEX. OUR FAX NUMBER IS 718-824-8362.OUR DIRECT EMAILADDRESS IS JRBBAUTO@AOL.COM

APO'S ORDERS WELCOME. WE SHIP ALL APO ORDERS US POSTAL PRIORITY.THANK YOU BILLY

B&B AUTOMOTIVE PARTS
1255 EAST 180TH STREET
NY,NY 10460

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Within a certain range of reason, O2 sensors are all the same thing. There is a catalyzed reaction that produces, generally, 0->1.1 Volts. This voltage is very mildly proportional to a:f ratio at the extremes of that voltage, and from about 0.3 to 0.7 volts the sensors simply act as switching units. That is also all any automotive ECU uses the O2 sensor for, as an on-off switch that represents leaner or richer than a 14.7:1 a:f ratio. With this noted, here are the other possible differences between O2 sensors: heater coil resistance and if the heater is grounded on the harness (4 wire) or to the body of the sensor (most 3 wires), plug style (solution = crimping since solder won't stick to the stainless steel wires), response time, and physical attributes of the sensor.

All O2 sensors I've ever seen (dozens and dozens) have the same thread and socket size, whether its a 1 or a 4 wire. Response time is not a concern at all since there are only a few cars on the road that adjust a:f on a cylinder by cylinder basis, and none of the cars represented here fall into that group (some new hondas do this). Response time on a normal O2 is in the range of milliseconds anyway.

The only real concern is the coil resistance of the heater circuit. If the car uses a relay to turn the sensor's heater on (my DSM does), then this isn't a concern. But, if the ECU switches this, you have to make sure that the ECU circuit is not being overloaded.

So the process then becomes finding the heater coil resistance on your current 3 or 4 wire O2 sensor with a DVM and then finding the cheapest possible replacement sensor that has the same # of wires that yours has. Measure coil resistance on this new one (at about the same ambient temp, don't measure a cold sensor and compare to a warm one!!!) and compare that resistance to the stock one. If they are close, splice the wires and you have a new sensor. If they aren't close, find out if your car switches the O2 heater on with a relay, of if the ECU does it. If the ECU does it, put the appropriate value 10W or so resistors inline with the heater circuit to match resistances. Using this process I found a borg warner 4-wire O2 sensor that was $19 and modified it to work in my car and give me my old, decent, fuel mileage back. It was a pep boy's product (pn OS140 or OS120 if I remember right) and coil resistance was about 4.5 ohms at 70 F.

Well, I hope my long-winded explanation here helps somebody save a couple of bucks. My real gripe here is with the auto industry, they charge a couple of hundred dollars for a sensor (V6 PGT) that must cost less than $2 to make. (Thanks to K.)