Check Engine Light comes on only when Towing

charlier180

charlier180

New member
Due to some Landscape work being done at my house, I have had to move my empty car trailer around.
A couple of weeks ago when I moved it off-site I noticed the CEL, VSC & VSC OFF indicators lights came on after I got the trailer parked.
During the parking process I had to perform multiple forward and reverse manuevers. During those maneuvers I notices the dash lights on.
I also noticed that when the transmission was in Drive the Reverse indicator was also on although not very brightly.


The CEL, VSC, VSC OFF lights stayed on so I made an appointment at the dealer to look into the matter.
After a few engine on/off cycles the lights went off before I could get to the dealer so I cancelled the service appointment.

Yesterday, I moved the trailer onto the new stone parking area that was built at my house. Once again the lights came on just as I spoke about above.
This time I noticed that after 4 on/off enbgine cycles the dash lights went out again.

I have the Toyota Platinum Extended Warranty which is good for a couple more years.
AFAIK, the warranty will not pay for diagnostic time if they cannot find a code and do a repair after the CEL goes out.
FYI, last October I had the Front/Rear/Center Differential Oil changed by the dealer and did not tow the trailer until a few weeks ago when the lights came on.
Not sure if that has any bearing on this situation unless something was not done properly during those gear oil changes.

Just wondering if anyone else here has experienced anything like this? I have to move the trailer again in about a week to take it for state inspection.
Before that trip I plan to borrow a code reader to see what CEL code is being set when the dash lights go on.
Hopefully that might provide some clue as to what is going on.
 
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If it a CEL is on and a code is thrown, that code should be in the computers memory. Swing by Autozone or something to have them read the code.
 
4boer said:
No help here but......are you using d or 4? Please let us know how it works out.
Click to expand...

Sorry I was not clear in my original post.

The CEL, VSC, VSC OFF lights stay off during towing until after I started to park the trailer.
In both cases, the CEL, VSC, VSC OFF lights came on after I had to shift the transmission between Forward and Reverse
a number of times and made some very sharp turns with the 4Runner while parking the trailer.

I did borrow my brother's code reader but have not had time to try to read the codes if they are still stored.
If the codes are not stored I will probably be able to read them next week when I take the trailer for inspection. Chances are the lights will come on.

BTW, when I tow I seldom, if ever, use overdrive. Many of the areas where I tow are far from flat.

I will post more information on this topic when it is available.
 
Used the OBD II Code reader last night.
It showed a code of P0705 which is : Transmission Range Sensor Circuit Malfunction (PRNDL Input)
Guess that explains the Reverse light also coming on when the shifter was in Drive.

Have an appointment at my dealer next week to have this situation taken care of.
Since I have to have my trailer inspected early that morning, I suspect that the CEL will be on when I get to the Toyota dealer that afternoon.
 
Same exact thing happened to me this weekend, I was towing my car all the way to oklahoma from dallas and when I got there the check engine light and vsc and some other dash lights lit up. I thought it was a fluke and disconnected the negative for about 20min. No more cels or lights but I was worried on the drive back to dallas hauling my car. Let us know what you find out.
 
4boer said:
Maybe bring the trailer with you to the dealer so they see the situation first hand. Good luck.
Click to expand...

If I run VERY late with the trailer inspection I may take the trailer along.
Unfortunately, I would probably have to drop the trailer on the outskirts of their lot as it is always packed with new, used vehicles for sale and vehicles in for service.

97hb said:
Same exact thing happened to me this weekend, I was towing my car all the way to oklahoma from dallas and when I got there the check engine light and vsc and some other dash lights lit up. I thought it was a fluke and disconnected the negative for about 20min. No more cels or lights but I was worried on the drive back to dallas hauling my car. Let us know what you find out.
Click to expand...

When the CEL came on in your 4Runner did that happen after you had to shift between Drive and Reverse a number of times to maneuver/park your trailer?
Also did you happen to notice if the "R" light was on (dimly) when you were actually in Drive ("D")?

You might want to use a code reader to check the code number that caused your CEL.
My situation has me thinking it might be time to buy a code reader of my own.
 
Towed the trailer this past Monday for State Inspection.
CEL did not come on. Took the 4Runner to the dealer to have them check out the CEL code.

Service Writer said that it is not uncommon for a trailer wiring issue to cause a CEL. As a precaution, they are ordering a switch for the shfter mechanism which will get installed in a few weeks.

Next towing trip is at the end f May so stay tuned.
 
1st post since being a member. have learned a lot from all the reading on this forum. had this same problem happen to me around Easter. i was doing some towing when cel, vsc, and vsc off light all lit up on the dash. also noticed the R light on the dash was dimly lit while in drive. I unhooked the trailer lights and unhooked the negative lead on the battery for a while. that cleared all lights. figured all was good to go although still felt a bit worried about hooking up the trailer again. well it turned out on my second trip in with a load of topsoil, while backing in the yard all the same lights lit up again and then my onboard computer and heater/ac controls burn out. at this point i had no clue what happened. i friend told me that the trailer must have some bad wiring and to ckeck all my fuses. did this and cound not find any. so i made an appointment at the stealership to find the problem. to make a long story short they called and said i blew a 15 amp fuse (ig15 i think, i don't have the dealer receipt with me). i guess i missed that fuse or something, i really don't believe them because my flashers still worked and the fuse that i blew supposedly controlled them. it wasn't covered under warrranty so it cost me 120 buck for tech diagnostics. that my two cents on the matter. i have expressed my thought with the follow up service rep and have not heard anything back. i guess before hooking up any trailer, the plug for the wiring should be checked for dead shorts. i did check the wiring on the trailer and it does have some shorts between the wiring, so i quess i have some work to do it. hope this helps.
 
I had this happen to me as well. I was hauling a trailer of stuff between Oakland and Sacramento when the light came on. I had no choice but to finish the trip out (it was another 60 miles) and check it out. Disconnecting the battery really only cleared things up for me for about 200 miles before the lights come back on. After taking it to my mechanic to check things out (in Califonria ... thanks to lawsuits ... AutoZone won't perform any CEL checks) and it turns out that there is a problem with my catalytic converter. I was told it would cost a WFS to repair but that it would really do any damage to my car so I haven't really worried about it. Now, once I get a job, I'll get it fixed but, for now, I'm not too terribly worried.
 
Just a thought, but it seems that everyone with problems had them occur while towing. The only apparent common factor, IMHO, could be the trailer lights connection. Though it could be a problem with the trans shifter electronics, as one dealer suspected, why would it only surface when a trailer is connected. I have had some corrosion problems with the trailer wiring harness on my '03, and had to re-wire the harness to repair it. Maybe simular wire harness problems are causing some type of electrical feed back to one or more of the ECM's and causing the erratic trans and engine CEL issues.
 
TechWrench said:
Just a thought, but it seems that everyone with problems had them occur while towing. The only apparent common factor, IMHO, could be the trailer lights connection. Though it could be a problem with the trans shifter electronics, as one dealer suspected, why would it only surface when a trailer is connected. I have had some corrosion problems with the trailer wiring harness on my '03, and had to re-wire the harness to repair it. Maybe simular wire harness problems are causing some type of electrical feed back to one or more of the ECM's and causing the erratic trans and engine CEL issues.
Click to expand...

:iagree:

Charlie and Frank, do your trailers have reverse lights?
 
Sorry guys, I forgot to update this thread last summer after the dealer repair and a few towing trips.

Yes, I do have reverse lights and I also have a backup alarm on the trailer (think commercial dump truck type "BEEPER").

Last May my dealer replaced the "Park/Neutral POS Switch Assembly" on my 4Runner.
The part alone was about $275 and was covered under my extended extended warranty.

Since that time I have not had a reoccurrence of the CEL and the dash lights coming on like I originally posted about.
I am still pulling the same trailer with the same wiring, beeper, etc. so it may be reasonable to believe that my problem
was indeed caused by the switch assembly they replaced.

Just wondering if the other people who experienced a CEL and Dash lights when towing got the CEL codes before resetting their lights??
My 4Runner stored the code even after the CEL reset itself after 3 or 4 engine stop/start cycles.
BTW, After I read the CEL code, I did not clear the code on purpose so the dealer could see the code for themselves.
 
I have a recently purchased V8 and a week old camper. Hauled it an hour to campsite no problems and on the way home today vsc light flashing. No other symptoms. Once trailer unhooked no more light. Not sure what the scoop is. Any ideas?
 
2007 4Runner with same issue. Error code P0705, Check Engine Light on, "R" light illuminated while in Drive, and traction control stuff all disabled.

For now I just cleared the code and I'll look again when it warms up.

Side comments: It's shista nasty cold out and there is a lot of freezing / thawing going on right now (condensation?). I've done my share of electrical mods, but most were done at least a year ago (something causing electrical stress on that harness). I don't have a trailer or pull anything.
 
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