P0705 Code and subsequent CEL issues

My 2007 TRD with 192K miles had a P0705 error code a few weeks ago. I had the Transmission Position Sensor Switch replaced by my mechanic, who switched off the Check Engine Light (CEL). A few days later, a neighbor backed his pickup into the side of my Tacoma and broke the rear taillight assembly. Fortunately, he didn't damage the metal. I ordered two new taillights and installed them, taking care to use dielectric grease on the new connectors. Afterward, the CEL came on again with the same P0705 code. Toyota has a technical service bulletin that recommends replacing a major part of the wiring harness if the code reappears after replacing the Transmission Position Sensor. Since this costs well over $2K at Toyota, I took it back to my mechanic to see if he could diagnose and fix the problem. He reset the code but the CEL came on again repeatedly, usually after 14 minutes. He solved the problem by FIXING THE GROUND WIRE for the taillights. I've read that some of the European and Japanese cars get strange check engine codes if the grounds are marginal. I hope this saves someone else trying to diagnose wiring harness issues.

 

Interesting my 07 also just started giving me this CEL code, I recently wired up my topper 3rd brake light and I wonder if that has something to do with it.

 

@ryanbitt

P0705 CEL

DESCRIPTION
The park/neutral position switch detects the shift lever position and sends signals to the ECM.

MONITOR DESCRIPTION
These DTCs indicate a problem with the park/neutral position switch and the wire harness in the park/neutral position switch circuit.For security, the park/neutral position switch detects the shift lever position so that the engine can be started only when the vehicle is in the P or N shift position.When the park/neutral position switch sends more than one signal at a time from switch positions P, R, N or D, the ECM interprets this as a fault in the switch. The ECM turns on the MIL and store a DTC.

The only tie in I could think of between this and the tail light assemblies would be the reverse lights. A short or a defective connection could cause a power loss and defective signals to the ECU.



You can check the Harness and the switch if you have a DMM

Check the Park Neutral Switch:



Check the Park Neutral Switch Harness:

 

Doing some research here related to this post. I want to put together a constant->momentary circuit and tap "Except P and N" off the back of the ECM to auto-lock my doors when going into gear. Does this idea present any immediate issues?

 

I wouldn't think it would cause any issues as long as the load isn't too large.

What I would do is use some type of optocoupler to isolate my home built circuit from the ecu.

https://www.electronicdesign.com/po...tanding-signal-and-power-isolation-techniques

 

Be careful, E8-30 terminal is for the A340E transmission


The A750E/F work a little differently, the voltage to the ECM E5-8 terminal and come through the start fuse circuit which is only hot while cranking the starter.

 

The ground wire in the rear tail lights is common for tripping the code for the 2015 Tacoma .
There is also a tech service bulletin for any Tacoma built before 2009
https://www.scribd.com/document/18857706/T-SB-0277-09

https://www.tacomaworld.com/threads...th-pics-for-second-gen-4-liter-trucks.289913/

 

Good info here Thanks!