Bosch o2 Sensor

1988 4.0 AT

My O2 sensor seems to not be working. I backprobed it with my Fluke 115 which usually is fast enough to pick up the voltage swinging back and forth. I'm getting a steady 5v. The old O2 is an NTK which lasted about 2 years so I decided to go back to Bosch and give them another try.

The new Bosch O2 is labeled pn 12009 on the box, but is labeled as LSH 24 on the body of the sensor. Is this the right part? I don't think it is. Looks different too. Engine runs rich slowly to lean until it almost stalls and then the computer gives little more fuel and the cycle repeats.

I'm going to send it back to Amazon. Any one else run into this?

There are many postings about The Jeep 4.0L not playing nicely with Bosch O2 sensors, and generic O2 sensors.

NTK is the original equipment and gives the best performance.

Early O2 sensor failure can be caused by contamination such as an excessively rich fuel mixture condition or oil blow-by in an older engine and engine coolant being burnt in the combustion chamber as a result of a head gasket leak.

Thanks, Tim. It looks like I've been replacing O2s every 2 years.

A steady 5-volts would indicate an open circuit in the sensor. The Renix used a sensor that varied it's resistance versus generating a voltage. 12009 is the right Bosch part number, but not sure if the LSH24 on the body indicates the right sensor type. You want NTK 23553.

Thanks. That is the NTK sensor that I'm replacing.

Denso’s are a good alternative to NTK. Currently running them with no issues


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I was "burning" through O2 sensors almost every smog inspection as well but I had always bought Bosch. They worked great in all my other vehicles. For my 2020 smog test, I switched to NTK and did a few other things listed below.

12009 is the one listed on Rockauto.

Along with the switch to NTK, I also adjusted my TPS, replaced my IAC, cleaned my fuel injectors (actually replaced them with clean/rebuilt ones), refreshed all grounds, cleaned my C101 connector and ran seafoam through the fuel, oil and TB.

While replacing the cap and rotor, I discovered a pile of dust and debris sitting under the rotor that used to be the cam sensor. So I replaced the distributor as well. So that, along with the usual oil/filter air filter, plugs change resulted in a PASS (with some very good numbers).

Last June (2022) I was up for testing again. I ran some seafoam, checked my TPS, and checked for any exh leaks. All was good. Passed on 1st attempt with some very low numbers. I haven't passed 2 consecutive smog tests since 2010-2012.

Not sure how much the NTK sensor contributed given all the other work in 2020, but I'm sold. Now it's just NTK and/or Standard sensors for me.

Well, the signal pin in the O2 sensor harness (engine side) was pushing back into the harness when I connected it. Problem solved.

Onto the next problem...