02 sensor ???????

[BlueRolex007]

Well guys i finally cut out the old 02 sensor out of my down pipe that the jackass previous owner welded in. I welded in a plate to my DP and replaced it with a brand new 02 sensor. And I still have a code 21, I checked all the wiring at the ecu for continuity and i even hard wired a wire from the signal wire on the 02 to the OX pin on my ecu and still nothing. :runaway:

Anybody have any advice???? Or something else i should try???

 

[BlueRolex007]

Bump anyone?

 

[CyFi6]

Are you getting a good signal at the ECU pin? Make sure the sensor is grounding properly.

 

[jetjock]

You're messing with the wrong wires...

 

[CyFi6]

Well in that case, you've got me. I thought that code was dealing with a bad or lost o2 signal voltage.

 

[bioskyline]

have you cleared the ecu?? could still be bringing up the old code

 

[jetjock]

Well in that case, you've got me. I thought that code was dealing with a bad or lost o2 signal voltage.

I was talking to him. Your advice is valid except a 21 is more often than not caused by insufficient current flow through the heater. It's even mentioned in the TSRM. Not that he used the book to check any portion of the sensor because, you know, RTFM is for pussies...

 

[CyFi6]

Well I was still partially wrong, I was unaware 21 could have anything to do with the heater circuit.

21 Oxygen Sensor Signal

Diagnosis
Detection of oxygen sensor deterioration.

Trouble Area
Oxygen sensor circuit
Oxygen sensor
ECU

That's all I see in the TSRM, which is rather vague, I figured there was a separate code dealing with the heater circuit, not to mention the code is titled "Oxygen Sensor Signal", which leads me to assume it is talking about just that- the signal circuit (OX) of the oxygen sensor. So 21 could mean that any of the 3 wires or sensor body ground could be suspect?

 

[jetjock]

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=26

I've never seen a 21 caused by the OX signal but since the book lists it I'll not going to say it can't happen. Nor have I seen a 21 caused by a low heater current on early model years.

 

[CyFi6]

Hmm good info thanks, I had completely forgotten about that page in the TSRM, I've been using the crappy engine error codes page on the Cygnus home page. Are you implying that on the early models you have only seen a shorted heater cause that code?

 

[jetjock]

Note that states for GTE only. There's also different DTC behaviors depending on where the car was meant to be sold.

I'm saying I've never seen a 21 on an 87 or 88 from any cause. It usually comes up on later models with an open heater circuit, wrong sensor, or the sensor unplugged. A for real short on any year results in a blown EFI fuse.

 

[CyFi6]

Very good to know. Didn't think a shorted heater would cause a blown fuse, figured the ecu would have some level of protection as 15A is a lot of current to be going through the HT ckt in the ecu in the event that the heater shorted. That is an interesting point though, a shorted heater could then cause the EFI fuse to blow anytime the criteria to enable the heater are met. Anyhow, I think OP should have no problem fixing his car now .

 

[jetjock]

I meant a short upstream. There may indeed be current limiting internal to the ECU. I suspect there may be since it monitors current within a window. Now you've got me wondering. Maybe we can get 3P to check it out and we'll both learn something :icon_bigg

 

[BlueRolex007]

So if im correct the 02 sensor has a signal wire, heater wire, and ground wire thats the 3 wires?