Hey guys, new to the forum. I've been troubleshooting, researching and trying to diagnose and repair this problem for the past two days, but I'm about to my wit's end.

Customer brings me the car, won't shift out of park. I immediately figured brake switch...checked and the brake lights work. I then checked ALL fuses in both fuse/relay panels. No results, so I swapped ALL relays under the hood and under the dash. No results. Next I went to interlock switch, checked and there was power, but no ground when the brake pedal was applied. Looked at the circuit and wiring diagram and noticed the TPS was tied into the system. I hooked up a Snap-On Verdict and checked to see what the TPS was reading. It said: 0. The shift interlock also worked with the TPS unhooked, so I figured TPS. My boss ordered a low-mileage used throttle body from local salvage yard. Put the TB on, still doesn't shift from park with the TPS hooked up.

Next, I hooked up my personal Snap-On MODIS. Checked value of the TPS and it was reading 10% at idle .51 volts. With the throttle fully depressed it reads 92% and 4.89 volts. So, I break out the multimeter again and physically go to the sensor. The sensor has a little over 5volts coming to it, ground is fine and it's reading (according to the DVOM) .49 volts butterfly closed, 4.91 open. I've also pulled the brake switch and checked it, both the brake light and cruise parts of it are showing continuity when they're supposed to and breaking connection when they're supposed to.

According to the diagram I have the ECM receives signals from the TPS, Brake Pedal Switch, and the Gear Lever Position switch, and has a negative output that triggers the Interlock Solenoid. The PCM/ECM is registering that the vehicle is, in fact, in Park when it's supposed to be, and all other respective gear positions for that matter.

I've got a pin-out of the ECU, was going to check and see what kind of values I get there, but I'm sure I already know the answer. My boss wants me to put it outside and start on something else, so I figured I'd ask on here. I've searched and everywhere either points to interlock switch or brake switch.

With the ignition key on, engine off or running I can unplug the TPS and the interlock switch will work when the brake pedal is pushed. I can plug the TPS back in, and the interlock switch will still work every time UNTIL I turn the key off and back on, then back to where I started. Somebody has to know what this is lol

 

Your tps value on your scanner is to high. it should be .49v as your multimeter shows. The tps value is a learned value in the ecm. check the throttle cable adjustment and see if you can adj it down to .49v on the scanner. If that wont fix it then reset the ecm and do an idle learn if your scanner will allow that. You can also try to take both batt cables off and touch them together, after that turn the ign switch to on. let it sit for 15 min. put it back together and see if it works. I wish you luck.

 

Thanks holmadk, didn't work so I figured the TB was bad...but read this...

Anyway, my boss calls Honda and they said "It's usually the brake switch" and though I had already checked both sides of the switch (brake light/cruise) and they both tested OK, he ordered a new switch. Put it in, same deal.

So, IAC motor was stuck open on the junkyard throttle body, but I didn't figure that would matter. I had a wiring schematic of the system and the ECM has 3 inputs and one output...throttle position, brake switch, and PRNDL switch are the inputs...if the TP reads the throttle is closed, the brake switch is pressed and the transmission is in park, it sends a ground to the interlock switch. If you're in RNDL it won't send the signal, throttle is pressed, brake not pressed....so this makes a little easier to understand.

Anyway, I had the interlock working with the key on engine off, as long as I didn't hit the throttle...If you tapped the throttle the switch wouldn't kick again until the key was cycled off/on. Also it would work until the vehicle was started, then nothing. Well, I swapped the IAC motor from the original to the junkyard TB, "unhook battery, touch terminals, wait, etc. I hooked my MODIS back up and the TP sensor was reading .49V with key on engine off, but as soon as the engine started it jumped to .51V. The modis didn't have an option to reset the ECM or Idle relearn, so I told my boss I thought it might be the TB or ECM, so he calls Honda and they said "Ya have to start somewhere. We'd throw a TB on it." He orders me a new TB and it comes today.

I put the new TB on, the problem is still there. So, I go to Alldata, look up the procedure for replacing the TB and there's a TSB regarding this matter issued in 2004 for 2003-2004 models. I was going to try to copy/paste it into this post but I can't log in from my home computer. Basically what the TSB said was "Car stuck in Park after TB change? Well, my friend, you're in luck because THIS is what you need to do" And as holmadk said, the ECM needed to be reset and perform Idle Learn Procedure.

BLAM, I hook up the snap-on Verdict and go into ECM, well, there's an option to reset, so I do...the Verdict said something about "now that you've reset the ECM, you need to start the vehicle, allow it to reach operating temperature and idle for 10 minutes with no accessories (Lights, radio, defroster, a/c, etc.) on. This is the Idle relearn procedure, so I do this and it's still not working.

I get BACK on Alldata and see if their procedure is different, it varies slightly but it's basically the same...theirs says "Reset ECM, start vehicle and hold at 3000 for 5 minutes and until cooling fans kick on (meaning it's reached operating temperature) then allow to idle for 10 minutes.

Well, here's the problem I think. The RELATIVE TP% needs to be at 0...doesn't matter that the ACTUAL TP% is 10...it's the RELATIVE TP%. According to Alldata, if the relative tp % is more than 0 with key on engine off, ECM reset and Idle Relearn need to be performed. Well, NO MATTER WHAT the Relative is ALWAYS 5%. I cannot get this thing to do an idle relearn.

BUT I think I know why, the car is idling between 1200-1300 RPM with the new TB...it was idling high on the junkyard TB when cold, but would drop to 800 after a couple minutes. I've checked for vacuum leaks...there's nothing but the TB gasket, and it's not leaking there. I FIGURED it was idling high due to the "relearn procedure" and that it would idle down to 850 once it was relearned...WRONG, 20 minutes of idling the 3rd try and I...grr...I guess I'm just not a Honda Tech. If I were, I'd know what to look for. IAC is commanded around 78 at idle. I've got too much time in this thing already...way to much, and we're losing money on it now. Bout to just send it to Honda and let them deal with it.

I tried the troubleshooter on the Verdict and it said that if the car is idling high at operating temperature and there were no codes set (and there aren't any), that either the throttle cable needed adjusted (which it doesn't) or there was a problem in the alternator (something...2 letters, I can't remember what they were off the top of my head) control circuit. eg check for fault in Alternator PD Control Circuit. It's the circuit that idles the car up if you hit the brakes, turn on the a/c or headlights or if the PS pump detects a high load.

Anyway, if you tap the brakes, the car idles up to about 1500 RPM.

I think ALL of this problem came about because the battery was CRAP...this car, come to find out, belongs to a car lot. They had just picked it up from the sale prior to bringing it to me...they left it sitting in front of our garage in neutral with the switch on...but the battery was shot long before that. AND the relearn procedure needs to be performed AFTER the battery is replaced, if it sits long enough...so. ANYWAY, the alternator IS making slight noise when it's cold...wow lol

 

Ps, sorry for the incorrect grammer, run-on sentences etc. I don't have the patience to correct it as the signal travels from my brain to my fingertips

 

The issue is resolved. I was thinking and decided that there were only a few things that would make the engine idle 500 RPM higher than normal both cold AND hot. Intake/vacuum leak, or IAC. I had made a gasket, because..well we ordered the TB from a Mazda/Honda dealership AND I work at a mechanic/body shop and one of the body guys checked in a large order, but didn't know the TB gasket went with the TB. So...I ran across the new gasket and figured I'd swap it before sending the car back to the car lot as a "couldn't figure out".

I pulled the TB, put the new gasket on, reinstalled TB and it was STILL idling 500 over and the shift interlock STILL kicked out and wouldn't come back on until the key was cycled off/on. I had left the intake elbow off of the TB, however (with the IAT sensor still hooked up as to not throw a check engine light) and it the IAC sounded like it was open entirely too far. I blocked off the IAC port with two fingers and the car idled down to 800, I guess this was enough to start the idle learn procedure, because after holding my fingers over the IAC port for maybe a minute, I pulled them off...the car revved to 2500RPM and began to slowly make it's way back down to 850. I allowed it to idle for 10 minutes after it hit 850, checked the relative TP% and it was 0 at idle or with KOEO (before, it read 5% at idle or KOEO).

So, I'm not sure if I just lucked into this fix, or if it might work for somebody else, but hopefully this information will help out in the future.

 

Could this repair cause the power locks to not work or need to be "re-set"? Have a good fuse and can "hear" the workings wanting to work but cannot lock electronically.

 

shift lock sol off

 

I signed up for this forum for the sole purpose of responding to this original post from a LONG time ago.

I also encountered this issue. Customer complaint was being unable to shift out of park, so he had to use the manual release. The other complaint was an aggressive jerk going from park to neutral. I also verified that the shift solenoid was fine and it was the engine computer that was not providing the ground circuit to allow the solenoid to release the shift interlock. The shift from reverse to drive was aggressive because the car was idling at probably 1,200 RPM vs the ~700 that it is supposed to. Vehicle would not even shift out of park with Key on engine off.

History: It's a 2005 4 door with something like 269,000 miles. Car is in great shape for it being 20 years old. Runs great, drives great. Everything works except perhaps a door lock actuator. Catalytic converter has a P0420 (discovered AFTER all of this diagnosis) He also has a 2004 Accord with something like 485,000 miles that is his "beater" car. Like he has done for many years, he would drive one car or the other depending on the seasons and blah blah blah. He took the battery out of his other Accord and put it into the 2005 model which has sat dormant in his garage for months. It started. It ran fine as usual. He drove it to work. When he left, that is when he could no longer shift out of park. There was no complaint up until this point. He drove it 45 miles to my shop, so it had notable run time on it by this point.

When I get the car, it has a P0122 (I think) which was TPS voltage low or something like that. I kinda ignored that and focused on the shift interlock and determined that the PCM was not providing the ground to activate the solenoid. The data PID in the scanner showed that it was receiving input from the brake switch, and the brake lights worked, so that should be all fine. I did some more research and found the original post here. I LOVE IT when people post actual test results and detail, but 99.9% of the internet says to "replace the brake switch". I found that the throttle angle was 9-10% according to scan tool data and the relative throttle position was 6 percent. Or was it 10 or 6 degrees? I cannot remember. I will go with percent. The spoiler alert is that it appears that this relative throttle needs to be 0% (or some value less than 6) before it will allow it to shift out of park. I tried making adjustment to the throttle plate and cleaning it, but I could not get the butterfly to close any further. It would mechanically bind up and that was it. The throttle position sensor is "adjustable" but Honda designed the fasteners in such a way that they did not want you messing with it. My multimeter showed 4.95 volts when backprobing the throttle position sensor. I never checked the ground side for integrity. The code was for voltage low, so an open there would cause voltage high...???

Ultimately, with my Autel, I did a "PCM reset" option with it. It fixed the problem. Idle speed came down like I would expect. There was no "idle learn" procedure in the scan tool. Then, as I was wrapping things up, I saw that the battery terminals were jirry rigged. The original terminals were bolted to a lead "universal replacement" terminal which went over the battery post. The car has been like this since he got it many years ago and was never a problem. There was no major visible corrosion on anything and the car cranked great. I didn't like this setup, so I removed the lead terminals and cleaned up the factory terminals which were in great visible shape and connected the battery. It would not shift out of park again and was idling high again. So, I messed with a few things again and came to no conclusion on any of it and did the PCM reset again with the scan tool. It fixed the problem. I then wanted to duplicate the problem, so I disconnected the battery, again hooked it back up and the problem did not return. I disconnected the battery for longer this time and used that time to put the center console back into the car, tried touching the battery terminals together, hooked up the battery, and the problem would not return. After all this messing around to ultimately doing nothing but a reset with the scan tool, the bill was getting high and the customer took me out to dinner. We drove his car, it ran great, despite setting a P0420. He dropped me off, and he went 45 miles home and is still happy.

Also, like one of the previous posts, I was able to disconnect the throttle position sensor, turn the key on, and then it would shift out of park. Cycle the key, and it would not shift out of park again. No noticeable rodent issues, and despite being a Minnesota car, it is clean and has not a lot of corrosion on it.

My best guess is that something else that uses the 5 volt reference voltage from the PCM to the throttle position sensor has an intermittent high draw or short and caused the P0122. With that, the PCM "learned" the throttle position voltage like this and caused this issue somehow. The wiring diagram shows the output shaft (countershaft) speed sensor using the same circuit, as well as the EGR valve. I always update my posts like this if there is any other news and I am able to find the post again, so additional information can be looked forward to.