Help with no hot start 2004 wj

[Rizno]

Helo, New member and have spent many days looking for a forum where I can find some guidance. I hope someone can help!

My 2004 GC will start up perfect when cold. It will sometimes start warm IF I press the brake when I am turning the ingition key ( meaning if i hold the key on start nothing will happen but the moment i step on brake it kicks over perfect) It will not start hot from the key at all.

I can however pull the starter relay from the power box under the hood and jump the connections and the truck kicks right over :\

The hot / cold issue is 100% consistent so I don't think its related to a loose connection. What on the Jeep would respond to the heat causing a no start? The starter is fine since it starts imediately when its cold and starts right up when i jump the relay. The brake bit gets me though. I can't imagine anything that would "allow" the car to start when i press the brake in "warm" situations. Would a nss be affected by heat? Or maybe a connection on the transmision that could be affect by heat and maybe expanding and losing contact? Dealership here in Ct. replaced the bcm under emissions warranty and this did not fix the issue. I needed my car back from them (they had it 2 weeks) so they weren't able to continue looking for the issue. I honestly haven't had much faith in them since the last try and am hoping to find help elsewhere!!

I really apreciate any help or even guesses I might get from you guys. Thank you.

 

[SteelHeadz]

I would check the ignition switch wiring first. Verify the power and ground. Since the ignition controls the shift interlock solenoid thru the brake switch, i would suspect that the circuit on that ground would have something to do with it.

 

[Rizno]

Grounds at those points seem fine after having a look. I didnt have my mm to check though. I did get it to pop a couple codes though, 1899 and 1698 they went away after 2 days of driving. Do you know what the contacts at the starter relay belong to? I imagine the nss and ignition switch. Is the nss 12+ or 12- when its in the "ok" to start position. (P or N)

 

[Rizno]

broke down and brought it in to another dealer.. So far they say: Rear drive axle seals are shot, TCM mal fuctioning and Range Sensor Malfunctioning. I asked if that would cause a no start only when hot and they said it's possible but not likely. They seem to think the hot start thing is a coincidence. So far I am not optimistic

 

[SteelHeadz]

What was the DTC for the TRS?.

 

[Rizno]

i didnt ask. They may have just run a diag on it? I assume you can with the tools? As far as the codes i've gotten it was just the ones I posted above . I also asked them to replace the door jamb wiring harness since mine was a mess and they said they wouldn't. That they would only solder fix the wires. Which I guess is fine but I really wanted a new one. The tech said they wouldn't do the job since it was a pita and would have to charge too much to make it worth it.....

Since the cars under extended warranty I dont really care if they replace sensors all day since it will be at no cost. My concern is that it's sitting there while they replace **** that isn't going to fix the actual problem I'm having... I asked if either the tcm or rs would be bypassed by me jumping the starter relay and he said no. Now to me thats wierd since I can start the car by doing so and I would think thats where you would begin when trying to diagnose the problem.... we shall see.

Ill keep this thread updated just in case anyone googling like I was, will be able to get some ideas if they have similiar probs

 

[SteelHeadz]

I would think that the TRS is worth the time looking at for the issue.
The Transmission Range Sensor (TRS) communicates shift lever position to the TCM as a combination of open and closed switches. Each shift lever position has an assigned combination of switch states (open/closed) that the TCM receives from four sense circuits. The TCM interprets this information and determines the appropriate transmission gear position and shift schedule.
There are many possible combinations of open and closed switches (codes). Seven of these possible codes are related to gear position and five are recognized as “between gear” codes. This results in many codes which should never occur.These are called “invalid” codes. An invalid code will result in a DTC, and the TCM will then determine the shift lever position based on pressure switch data. This allows reasonably normal transmission operation with a TRS failure.
If the TRS test is performed and the park pressure switch fails, the likely culprit is the TRS.

 

[Rizno]

Good Info! Will an invalid code cause a no start?

Also since I still havent gotten an answer to this question.. schematics on autozone.com seem to point to both the keyed 12v and the nss 12v going to the starter relay which when switched pulses the starter. What would break that routine? I can start the car by jumping the relay (shorting the starter leads) so either the nss lead or the switch lead is not active when I have a no start situation. Would the trs/tcm failure cause the nss to not send an "ok" singal to the starter relay?

Thanks SteelHeadz for your attention

 

[SteelHeadz]

The TRS is an input to the PCM. The message is communicated thru the bus to the TCM to determine the TRS position.

Check the ASD relay as well . This relay will disable the starter relay if there's a fault in the starting sytem.

Here's the diagram for the Starting system.

Out of curiousity. does it start in the neutral position?.

 

[Rizno]

Good info there

No it wouldn't start in any position unless I jumped the relay.

Just got the call for pickup. They say it's starting perfectly after being driven and leting the engine got hot. Going down now to see. Will post back after.

So to recap. They replaced the TCM and the Range Sensor and their guess is that after driving the car the sensor was "locking out" in drive or whatever gear and not allowing a restart. The only problem with that is the car would start after sitting a while.... so let's wait and see.

 

[Rizno]

Okay, couple weeks have passed and everything seems to be good!! So either the TCM or the RS either or both were causing my issues. Happy it's fixed, no more embarrassing starting the car from under the hood lol.

thanks SH for the pointers!