Overdrive lockup problems

Hello guys long time no post from me, sorry but I have an issue on my 2001 Grand Cherokee that I am hoping someone can help me with. This is my wifes daily driver.

start the car and hit the switch for OD and nothing happens. Now heres were it gets weird, I hit the brake pedal and the light switchs on, if I hit it again and it switchs off. But wait, its even weirder, If I push the brake pedal, and then hit the switch it will turn on and off. Makes it a pain to drive, everytime I hit the brake I have to hit the switch to turn it back on.

I have changed the brake light switch, and the TPS, neither made a difference. This all started after I put the new head on. Doesnt matter if its cold or hot, so I am at a loss and hoping someone can help. Trans pulls fine and shifts perfect. Thanks in advance guys:tears:

http://www.cherokeeforum.com/f5/kickdown-cable-adjustment-95421/


Maybe?

I've tried that, but the problem is this occurs even if your just parked

Just a WAG (wild arsed guess) but it sounds like a ground issue. I'm not sure of the ground positions on the Grand. You said you put a new head on, I'd ohm the grounds from the head and block to wherever they go.

Next best guess would be an oil covered connector which could lower the working voltage enough to be an issue.

Agree, you are very likely looking at a grounding issue due to the symptoms you described. They can be tricky to track down, but use your FSM to learn where they are and then systematically check each one for security and cleanliness. Remove and clean off any corrosion if necessary.

Ok thanks guys, I'm headed to the garage now. Let's see what I find

Well so far no luck, cleaned all the grounds, checked the plugs.

You really have to ohm test the grounds or better yet put your meter on DC voltage and test the ground circuit (from the wire and not the connector ring) to battery negative. You may have what is commonly called standing voltage. Standing voltage is residual voltage in the/any ground circuit that gets backed up from excessive resistance.

Pretty common in the TPS ground, can be in any circuit.

The ground rings can corrode where the wire connects/crimps to the ground ring. And the worst one is the copper core of a wire can fatigue from vibration under the insulation and break where you cant see it.

The speed senor, the TPS and brake switch likely all contribute to OD and/or torque converter lock up. The kick down cable with also unlock the torque converter mechanically.

I don't know if the holding circuit for the OD is external (a relay) or internal in the PCM.

Could be something as simple as the OD switch being weak. Switches get flash deposits on them, heat weakens the springs, the contacts themselves ablate as they are used and age. Most contacts are coated brass or alloys, once the coating ablates or wears off the resistance can increase.

I tend to look at bad connectors before anything else, they screw up a lot. The male or female part of the connector contacts can back out of the holder. The connector contacts can heat up, relax and make poor contact. One quick tip off is a good flashlight and look for discoloration on the connector contacts.

I usually troubleshoot from easy to hard and from cheap to expensive. Way to often swapping out parts hoping to get lucky is just a waste. Sometimes you can bypass all the time intensive testing and head straight for a likely culprit, most times you are replacing serviceable parts with new, but not necessarily better parts.

One note to point out, it started working right a few weeks ago, but when I pulled the dash to replace the heater core it went right back to acting up again.

Looks like I'll be back at it again this weekend.