2002 TRD 4WD Tacoma in limp mode for the forth time

My first post on this forum.

I know you will tell me I need a scanner. It’s on order. The first time in Limp Mode I was able to clear it by pulling the battery. The second time there was no Check Engine light and no codes. I took it to a reliable shop they cleared it and were unable to recreate the problem. I replaced the TPS, cleaned the MAS and the throttle body. The third time it went in limp mode there was a CE light. I took it back. The scan indicated that it was a shifter position sensor. They replaced it. Today it went back into LM and the CE light is back on. Its becoming apparent that the codes being pulled are not to be trusted. Any suggestions? I’m already into this problem for $600. Any suggestions besides the dealer? Anybody have a sure fire way to clear limp mode. The last time, disconnecting the battery did not clear it. its currently sitting in the drive with the battery disconnected

 

Be curious to see the codes you pull; you know those code readers can be had for $15-20 at a local parts store and Walmart even.

Knock sensor issue could put your vehicle into limp mode.

Anyway, we'll wait and see once you get your code reader in; throwing money at a vehicle without proper diagnostic is just an easy way to separate you from your cash.

 

I pulled a P1780. park Neutral switch. That was just replaced I see a number of threads concerning that code on this forum. Seems it may be related to a tail light issue. My truck does have a spliced in set of trailer lights that haven't been used in 15 years. If it weren't raining like hell and 40' out i would be investigating. I'm afraid my garage is not available. My 71 Alfa Romeo is in there. (Its never seen rain in the 15 years I've had it I'm afraid it might try to run away if i get it wet.) Tomorrow is going to be cold but no rain. I will see about it then and post an update. BTW I love auto forums. I spent 4 years building the Alfa from a true barn find, all with the help of the Alfa Romeo forum. I have used this forum in the past as a guest and always found sound advice I suspect I will be visiting more as my truck passes the 20 year 190K mark. Its been solid for all those years. Like my Alfa it has zero rust and has always been reliable. ( i can hear you all snickering about a reliable Alfa Romeo but I assure you if you do it right, and keep Non Alfa mechanics away from it, they will run forever. ) My only other issue with the Taco was a spark plug that backed out and bunged up the threads requiring a heli coil. Not bad for 20 years.

 

Alfa pics?

 

I would but I haven’t figured out how to do that on this forum. It’s very easy on my Alfa Bb but the two are not the same

 

Thanks for asking. It was a labor of love.

 

Yep, I had this code (I think). although mine was a "no shift" issue, I could rev it to redline. turned out to be a bad relay to ground.

check your lights when parked, see if any come on while the running lights are lit

 

It would be ironic if it where a bad relay. My Alfa Romeo had zero relays when new. It was the reason the electrical system was considered so unreliable. I installed relays on all the major components. Headlights, starter etc. it was hard to believe but the current to the starter actually passed directly through the ignition switch, thus they often failed. There is no real wiring harness on the car. Every circuit was run individually. Grounds are often an issue, especially on rusted cars. Since mine has never left San Antonio that’s never even a problem.

I intend to read every thread on the p1780 issue before I dive in today. I haven’t noticed any problems with my light but I seem to recall that the lights where off when I got it back from the shop and that I turned them on on my way to HD. The CE light and limp mode happened on my way home

 

I think the little Japanese gremlin has been found. It was so bizarre. Here are the symptoms and findings.
I removed the trailer light harness, which was not cut in but was plug in. That had zero effect.
SOOOOO
key on, lights on.
tail light on passenger side= brake light and backup light on
tail light on drivers side = tail light on but very very dim
moving wiring harness around and swapping tail lights created a whole other set of bizarre combinations of tail light and blinker on/off.
I discovered there was a loose wire in the connector on the rear of the passenger tail light. I cut, soldiered and reinstalled the wire. It had zero effect except that moving the wiring harness no longer created a new combination of light on/off. One issue solved.

Cleared the P1780 code.
discovered that with headlights off all lights function normally. I believe that the only place that all the lights come together is at the headlight/blinker switch.
I have ordered a switch.
Code stay cleared BTW
Did I mention earlier that the truck went into limp mode after i turned on the headlights?
I'll post the result when the switch arrives
It is just so odd that both the blinker switch and the window control switch (went out 3 weeks ago) both failed within weeks of each other.
These Japanese gremlins are tricky but not as cruel as the Italian ones. The Italian gremlins demand the appropriate blood sacrifice before revealing the solution

 

Trailer lights are my guess. I had a similar issue when I put on an offroad bumper. I went 4 wheeling in the rain after this bumper was on for 3 or 4 months. Got a brake override malfunction error. Once I shut the truck off, I could not start it. I am on a trail in the middle of nowhere. Luckily I have just enough cell signal to look up the error. Looked here.. Looked on the internet forums elsewhere.. Looked on Youtube.. Guy on youtube had same exact issue and it ended up being the 10 amp STOP fuse under the hood was blowing due to an electrical short. Fortunately I had a 15 amp fuse to replace the 10 to get me off the trail. That allowed me to start the truck.. but soon after as I was driving the error came back. I was able to get the truck home. So I continued to research what was going on.

For the next few days I would replace the fuse which would clear the error, but soon after driving 5 or 10 minutes the error would come back.

After determining it wasnt my brake lights which were aftermarket, or the backup sensors which I did not hook backup with the offroad bumper.. I pulled the plug on the hitch. It was not completely locked on the clip which allowed water and mud into the plug. I don't tow anything at all so I disconnected the plug from the hitch. Didn't want to cut it so I allowed it to dry and just taped it up to test it out. Since I have done that I have had zero issues at all. That hitch plug was causing a short in the wiring harness. Have not hooked it back up yet but plan on it soon and will make sure it is properly connected and taped up to seal any water from getting in.

If you have some exposed wiring in the rear harness I would make sure all that is fixed. Otherwise you will be chasing gremlins. Fortunately for me I only had 2 things it could be even though I checked the tail lights and light bar in the front of the truck. The last 2 mods were removing the backup sensors and that hitch plug.

Anyways best of luck!

 

New turn signal switch arrived today. It made no difference I am disappointed to say the least. I had all the exact same symptoms with the new switch.
As long as i don't turn on the headlights everything is copacetic. Turn the headlight/tailights on with the truck running and it goes into limp mode and the tail, brake and backup lights all go crazy. I honestly can't recall the last time i drove this truck after dark so for now I may have to walk away.
Its not the switch, Its not the trailer lights. I'm not certain a wiring diagram would help.

 

Sounds like you have a bad ground in the headlight circuit- Most things on these trucks are ground switching.

 

I had a similar situation.....
.....turned out to be my ignition switch.....

am2 part of switch was going bad.....allowing to start.....but then pop am2 fuse 4 or 5 miles down the road.....would blow when you give it extra gas.....

am1 side on that switch affects all those other systems you mentioned.....

 

Sounds like i need to find the ground points for both the headlights and til lights My guess is the grounding issue is in the rear as that's where all the odd lighting issues seem to be. Should i be looking for a ground location on the frame?
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