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Toyota Service
Toyota Service, Lexus and Toyota expert
Category: Lexus
Satisfied Customers: 4605
Experience:  30 + years of experience; Multiple Award Winning Svc Mgr; Just Answer Customer's Choice Award Winner
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Ok so I have a 1992 Lexus SC400. I started getting the code

Customer Question

Ok so I have a 1992 Lexus SC400. I started getting the code 55 which is the driver side knock sensor. I bought some cheap knock sensor and some used plugs at the junk yard and put them in and used butt splice connectors to connect them. That gave me a knock sensor code for both sides after fixing it. I later found out that you cant do that with knock sensors because of the low voltage. The knock sensor wire harness is part of the complete harness on this model so buying a new "knock sensor harness" is not an option. I bought so new good quality knock sensors and two knock sensor plugs from Toyota. I now need to know how to effectively reconnect the wires.
I also have engine code 21 which is a left main oxygen sensor. This is the driver side of the car. I bought two new main O2 sensor and installed them. This did not fix the code. I swapped both main O2 sensors with each other in hopes to see if the one I bought had a defect. The same error code read out. So its not the oxygen sensor. I had noticed the left connector was covered in oil because of my engine oil leak so I got electrical connector cleaner and attempted to clean the connections but this didn't fix the code either. Then I thought it was the ECU so I bought a new "tested" one and that did not add or take away any error codes so O figure my current ECU is still fully functional. I am running out of ideas I need to get these fixed.
Submitted: 8 months ago.
Category: Lexus
Expert:  Toyota Service replied 8 months ago.

Hello. Welcome to Just Answer. Please allow me to assist you. This sounds like you have one problem causing another. If the knock sensors are reading incorrectly, they will retard the timing on that side of the engine. If this is so, your left side of the engine is being leaned out. Assuming that the wire connections are all good, the oxygen sensors are genuine Lexus replacements (aftermarket/Non-Lexus sensors can and will give you these fault codes), and the ECU is good, I would be considering re-examining your knock sensor issue. The proper way to rectify this is with a complete engine room harness. The reason for this is when you encounter a connection, or a splice it the wires, some of the amplitude of the knock frequency is compromised ( "knock" in the engine vibrates a piezo-electric crystal inside the knock sensor. This vibration is transmitted to the ECU, where the ECU moves the timing to reduce pre-ignition, which is "knock"). Before I went and got an entire harness, I would seriously consider stripping the wires back and hard soldering the connections where needed, and then apply heat-shrink tubing over the solder joint to protect it from shorting out. This is def worth a try, and might save you a wire harness replacement, and, if the knock sensors are then transmitting properly, your oxygen sensor might disappear.

Expert:  Toyota Service replied 8 months ago.

Please confirm that you have received my input. If you have any questions, please feel free to ask. Thanks.

Expert:  Toyota Service replied 8 months ago.

If you have any questions Please feel free to reply

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