P0115 , P0420 codes help

I have a 1999 Tacoma 4x4 2.7ltr. Over the past 2 weeks when I start my truck, after it running for about 1 or 2 minutes it would idle up for about 3 to 5 seconds and then back down to normal. No check engine light or anything. Just the high idle for a few seconds ( about 1200 RPMs ). Then the check engine light came on. It would still crank and run fine. The codes are P0115 and P0420. I replaced both Temp sensors, on the back of the block and at the fron of the block. The code went off for about 15 miles. Then it came back on , same codes. I've read through the forum and it seems that there is a running issue or no start that's common with the Temp sensor issue. Mine has never had a problem starting or running. Is there anything else I can check to see why the problem still exists? Thanks guys !

 

P0420 (bad cat, O2 sensors, exhaust leak). Check your exhaust manifold for cracks. Up till 2000 had cast manifolds that crack eventually. ‘02 2.7l changed to pipe manifold. I did manifold conversion to solve my P0420. Better low end performance afterward. Tape a shop vac to tailpipe and spray unions with soapy water to find other leaks. Good luck. Can’t help with P0115 or if/how it could be related to P0420.

 

I did pull the CAT off and inspect it. Both my 02 sensors are about a year old. I had no idea about the manifold issue with these models. I guess I need to inspect the manifold. I'm just not sure why the P0115 code came back after both Temp sensors where replaced. Thanks for the reply. I'll check my manifold this weekend!

 

I agree with THatt….unrelated
Unless
The exhaust leak melted the ECT sensor harness somehow

 

Exhaust leaks seem to be most common cause of a P0420 code for these tacomas. Was the case for me. Search some videos on how to identify an exhaust leak. No experience with the P0115 code.

 

Thanks for all the input everyone. The plugs and wires all look great. Not to say that there couldn't be a wire rubbed somewhere. It runs great and no loss of power. The idling up has went away since I replaced both sensors so I'm probably just going to drive it and see if any other symptoms come up.

 

Sorry for the lengthy URL's

I suspect that there is an open circuit between the 2 pin coolant temp sensor (ECT) and the PCM. I am assuming you have a scan tool. I also suspect that the PCM is going between open and closed loop operation, depending on if the ECT signal is being read by the powertrain control module (PCM). When the PCM does not get "expected" inputs from the sensors it will use stored data for engine operation, and IMHO, that is why the idle up situation.


https://charm.li/Toyota Truck/1999/... (For Computer)/Diagrams/Electrical Diagrams/

https://charm.li/Toyota Truck/1999/...gine Control Module/Diagrams/Connector Views/

 

Would this be a wire harness issue or still possibly the plug itself ? I tempted to just replace it and see if it works.

 

Impossible to tell without testing. If you back probe the connector at the plug and back probe the connector at the PCM with both disconnected with an ohm meter and wiggle the connector and the meter goes out of range intermittantly I would say ECT connector. You need to back probe these connectors, if you jam the meters probe into the front of the connector and spread them, you are screwed.