O2 Heater code

Last weekend, on the way to Devils Lake, the bracket that holds the wires for the downstream O2 sensor fell off the chassis. The driveshaft then ate the O2 sensor wires and make interesting sounds inside the cab

After tucking up the wires we continued our trip. The symptom that showed up was poor running between cold start and normal operating temp which lasted a short time. The Jeep also though 2 codes, a downstream O2 failure, and a O2 heater failure.

Today, I spliced together the O2 sensor wires, and that cleared the downstream O2 sensor failure, but not the heater failure. The symptom remained the same.

I did locate the O2 heater fuse in the PDC (fuse box) under the hood, and replaced it as it was blown big time! It is a small blue 15 amp fuse in the row near the relays (unmarked by the factory).

That cleared all codes, and things are back to normal. I bring this up because many of our vehicles are OBDII complaint and have O2 sensor heaters. This could be a problem one sees on the trail if the downstream O2 sensor wires get damaged (or that darn bracket falls off )

-Ron

Yep.

Note that all of our O2 sensors have been heated since RENIX days, so this doesn't just apply to OBD-II. Thus, HEGO (Heated Exhaust Gas Oxygen sensor.)

The sensor was originally unheated (EGO - Exhaust Gas Oxygen sensor,) but the heating element was added in short order as it could take upwards of fifteen minutes to reach operating temperature - which is somewhere around 700*C, as I recall. Adding the heating element shortened the warmup time to something like 2-3 minutes, taking the engine out of Open Loop operation that much sooner and reducing HC and CO aggregate emissions as a result (just like trying to improve catalyst light-off times.)

I am in the same boat, any idea which white wire goes to what? there are two of them. My Haynes manual diagram has totally different colors?

I guess I actually need to know what wires go to what so I can splice them.

jwalter04 said:

I am in the same boat, any idea which white wire goes to what? there are two of them. My Haynes manual diagram has totally different colors?

Click to expand...

You're a bit thin on the details here. I'm assuming we are talking about the 99 mentioned in your user profile, and the upstream sensor?

On a universal O2 sensor, the two white wires are for the heater. It doesn't matter which is which. One should go to the black wire (ground) and the other to the dark-green with white stripe wire (ASD Relay). The bosch black wire should go to the black with dark green stripe wire (O2 signal). The Bosch grey wire is the sensor signal ground and goes to the brown with yellow stripe.

Sorry, yeah it is the 99 sport in my profile, however I don't think it is the upstream sensor ( if it matters) It is the one after the cat next to the transfer case. Some further info

The wires coming out of the sensor are White, White, Grey and Black

The wires coming out of the harness are black, green w/ white strip, tan w white strip, and brown w/ yellow strip


Could the black w dark green strip you refer to be the tan with white that I have.

Yes, the color are the same except the signal wire is the tan-white instead

So, for the 1999 downstream sensor then, the Dark-green with white stripe (ASD Relay) and the black wire (ground) are the heater wires. Those would connect to the white heater wires on the sensor. The brown with yellow stripe (sensor ground) would go to the O2 sensor grey wire. The tan with white stripe (sensor signal) goes to the black wire.

Just bumping this because it helped me out a little bit. I didn't know that 15A fuse existed.

1998 cherokee sport 4.0
-surging, rough idle, no power in low rpm
-CEL gave 3 codes, high voltage on both oxygen sensors, and bad heater
-replaced oxygen sensors and CEL was still on, throwing same 3 codes, problems still there
-replaced 15A fuse and CEL went out
-still have surging, rough idle, no power low rpm but CEL is gone and I wouldn't have figured it out if not for this

I'm going to try and check TPS, IAC and CPS for issues causing my problems