Tow haul light comes on as soon transmission is shifted into gear

Good morning,

Are there any codes in the system for the transmission?

https://www.2carpros.com/articles/automatic-transmission-problems

Does it shift well while driving?

Roy

Yes, if overdrive is not actually engaged (even tho light is on). If it's actually in overdrive, it doesn't want to work up thru the gears to accelerate.

Okay, can you check for any codes?

There is a fault somewhere.

Roy

I am not a mechanic, justt the owner. So no equip to test. Guess I'll have to take it in and leave it running next time it does this, so they can check it for codes while the light is on?

A parts store will read them for free.

Once I get the codes, I can narrow the area of failure down for you.

Roy

Thank you. I will take it out at lunch tomorrow and if it's doing it, get a store to read it for me. I've had them change batteries, and headlamps but didn't know they'd check for codes. Thanks for that tip!

You are welcome.

Keep us updated with the results.

Roy

Here is a guide to yelp you get the codes. but it sounds like the tow/haul button/switch is bad have you try cycling the switch?

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Please run down this guide and report back.

Thank you Ken. I have ordered a code reader. Had no idea I could do it myself! Very helpful article, and I appreciated the link to the codes in the article so I didn't have to buy a reader that tells you their description. Will be back in touch in a few days.
Also, if you will tell me how to "cycle the tow haul switch," I will try that too.

Good work, cycle the switch mean to push it on and off many times to see if there is a change.

When you tow heavy loads, it is recommended to turn it on. it disables the clutch converter in the torque converter to put less pressure on the transmission. Otherwise, you could damage the clutches. Those clutches are the least amount in any clutch pack and can easily be damaged if they are over worked by the heavy load.

Roy

I've gotten the code reader. Used it this morning. No codes, even though tow haul light came on after cranking. Is it possible the tow haul switch wire is going bad? I saw some YouTube videos about it breaking after flexing so much during use.

Okay, what is the brand code reader you got?

Some of them will not read anything but engine codes. They will not read any other system.

A quick test you can do is this. Run it up to 55 MPH and with your foot on the gas, let the other one touch the brake pedal and see if the transmission downshift.

If it does, then it was in overdrive. If it does not downshift, it will not change at all.

Roy

I bought an Actron CP9125 OBD II PocketScan.

Okay, thanks. That just reads the engine system. It will not read ABS or any other module.

Did you do the test I suggested with driving?

Roy

Will do that later today.

Okay, keep me updated with the results.

Roy

Did the driving test you suggested several times. It did not downshift, unless I really pressed down on the brake. Also, it hasn't gone straight into tow haul mode after cranking and shifting into gear, in several weeks. It has been very warm in the mornings, like mid high 70's, so I wonder if air temperature makes a difference?

Are there any codes set?

Roy

Will check when I leave work this afternoon.

Sounds like a plan.

Roy