Adiaz8813

Hey guys so I just recently purchased a 92 SC300 2JZGE and the previous owners decided to cut the o2 sensor wiring and just had the wires loose in the engine bay. I found a single white wire by the alternator and a single blue wire located closer to the throttle body. I thought there would be atleast 3 wires for each o2 sensor...? I ended up splicing the single wire to the signal wire on the o2 sensor but I'm still getting a CEL 27. The car is also idling high and as soon as I put it in drive it will drop down and almost die. I've verified there are no vacuum leaks and that the MAF and TPS sensors are working properly. I've also repositioned the TPS to spec. If anyone could please post a picture of their wiring to each of the upstream sensors or tell me how many wires there are coming from the car itself I would highly appreciate it. Thank you in advance.

oldManTan

there should be 4 wires for each sensor. 2 wires for the heater and 2 wires for the signal and ground. they are self heating O2 sensors. code 27 is for the Sub O2 sensors which are after the cats though and those have 4 wires as well. those wires should be in the footwell though under the carpet, nowhere near the engine bay.

KahnBB6

iTrader: (5)

^^ If the OP has a 1992 SC300 regardless of emissions spec those front O2 sensors will only be two wires each meaning non-self-heating types and the ECU will not be looking for self-heating four-wire type sensors up front on the header.

Four-wire heated front O2 sensors didn't show up until 1995 CA-spec and 1996 Federal+CA.

1992-1994 SC300's with CA Emissions all have 2x front O2 Sensors with TWO wires each and one 3rd O2 sensor under the car with FOUR wires (meaning it's heated).
1992-1995 SC300's with Federal Emissions all have the same 2x front O2 sensors with two wires and NO 3rd O2.
1995 SC300's with CA Emissions and all 1996-2000 SC300's with Federal or CA Emissions all have 2x front O2 sensors with FOUR wires for the self-heating function and a 3rd O2 sensor under the car that is four-wire (self-heating).

I happen to have a set of OEM Denso O2 sensors for a 1992-1994 SC300 handy at the moment if you need reference pictures of them.

OP, did the previous owner cut off the front O2 sensor connectors on the engine harness side? If so we'd need to get you the replacement connector and repair terminal part numbers so that you can get them back to normal again.

Adiaz8813

Thank you very much Kahn that's very helpful. Yes so they did cut the harnesses on the engine side but I'm only seeing 1 wire for each upstream o2 sensor... I'm assuming the 2 wires that should be there would be a signal and a ground correct? I will definitely have to get a replacement connector for each of them. At the moment I believe they are working with the single wire being spliced cause I'm not getting a CEL. I am getting a CEL 27 for the downstream sensor signal which is because there is no sensor there anyways. I'm reading downstream o2 sensors shouldn't affect your idle or performance but I feel like they would be just as important as the upstream sensors. If I were to modify the exaust so that there is a place for the sensor would I cause myself issues due to the car not having cats? Thank you.

KahnBB6

iTrader: (5)

If your SC300 is a Federal 1992-1995 model you simply won't have the necessary wiring on the body loom to received a 3rd O2 sensor signal. It sounds like your SC300 is a 1992 CA Emissions spec or else one of those type ECUs was swapped in at some point by a previous owner.

The 3rd O2 sensor that is heated with four wires does not influence the engine running, adjustment or calibration. It is simply an "efficiency check" sensor to alert if the secondary catalytic convertor is going bad. It communicates with the ECU and the dash CEL code that would result from it detecting operation of the range the ECU expects from it is the only thing that happens in the event of a malfunction, bad cat or with the cat and sensor removed in that location under the car.

Yes, if you just put the 3rd O2 sensor in there with no cat it would likely be triggered. There is such a thing as an "O2 sensor simulator" that I have heard of in the past but that's a DIY thing I don't have any info on, sorry.

For the two front O2 sensors on your 1992 there should be a main sensor wire and ground for each, yes. I'd have to check and post the relevant wiring diagram pages. My guess is that the previous owner snipped off the ground wires and taped over them for whatever reason.

The connector ends I can identify for you shortly. I have a spare 1993 2JZ-GE engine harness that I can read the connector part numbers from. With those it's then possible to identify which terminal repair wires are needed for them. Since your O2 sensor ground wires were likely trimmed back a bit into the harness you will probably need to add some new wire in the correct gauge to repair them once you can measure the missing distance from your new terminal repair wires with your new connectors.

RXRodger

iTrader: (2)

Also note the signal wires are shielded.

KahnBB6

iTrader: (5)

Yes! Thanks for mentioning that, RXRodger. The signal wires are shielded up to the connectors themselves so that will have to be recreated as well or pilfered from another Toyota harness with the same gauge shielded wiring.