Hello:

'04 Accord EX, 4 cyl, auto, 67k miles. Bought this car in Feb after I totaled my '04 LX. There were no problems until early August.

Started it one morning and it went on high idle at 80+ degrees. It came down after a minute or so, but didn't seem sure it wanted to stay there. Drove it to town and it was miserable. Delayed up-shift. On the highway it would hang onto 3rd for miles, would drop into 3rd or 4th at a slight hill where it had never hesitated to stay in OD. Could 'encourage' it to shift up by accelerating and then abruptly backing off the throttle.

In town, it would drop back into first late and it seemed to jump forward at the same time. This little quirk was abrupt enough to be alarming in traffic.

At about the same time, the shift lock solenoid failed, so I had to stick the key in the little slot to get it out of park. A month down the road, I still forget 99% of the time.

The following week, when I went to town, I took it to Advance Auto and borrowed their scanner. The only code that came up was: 'throttle/pedal position sensor A circuit low input' There were also '$09' and 'P0122' in the display.

I checked the output of that sensor with a meter and it seems normal... about .5 v to about 4.5v, and smooth output with steady motion of the throttle.

As time passed,the symptoms became less noticeable and by now have almost disappeared. It still drops down into first gear a bit rough, but not nearly as rough as before, and the OD doesn't seem to want to engage fully about half the time. Some days it will shift very late on accel, others it's fine.

I checked the brake pedal switch, it's fine...both halves. There is no voltage to the shift lock solenoid. The solenoid works if I hook it up to 12V. I can't find what powers the solenoid. it's like the orphan child in all the schematics in the Honda shop manual.

So I have two problems, possibly related.

Intermittent cold idle and shifting issues that are just bad enough to let me know that all is not well.

No power to the shift lock solenoid.

It may be worth noting that the '04 LX I mentioned developed the exact same set of idle/shifting symptoms a year ago. It had 120k miles including maybe 7k pulling a trailer. I don't think that the shift lock was involved. Don't know any codes related to that one. Never got around to looking. Those problems cleared completely on their own. Is there something that happens to 10 year old accords?

Can anyone help me figure out what's going on?

Thanks
Craig

 

Suggest resetting PCM and see if same code P0122 returns. If yes, diagnostics are indicated to determine if electrical fault is TPS sensor, connector, wiring, or PCM fault.

TPS fault might affect shift quality, however if towing has been performed, I would suggest starting w/ an ATF fluid change (drain/replace). Towing can cause overheating and rapid aging of ATF.

Shift Lock Solenoid should always be hot w/ ignition switch On. If 12V missing, check fuse 21 (7.5A) in under-dash fuse/relay box. If fuse is good, look for a wiring or connector fault.

good luck

 

Possible culprits for not being able to shift out of PARK:

• Blown fuse

• Wiring issue - short or open (break) in wiring

• Brake pedal position switch

• Throttle position sensor - Try unplugging the connector to the TPS, you’ll get a Check Engine Light; but, see if you can shift out of Park.

The voltage needs to be at less than .5 volts (this essentially tells the PCM the accelerator pedal is not depressed and the throttle is closed). If it is at a higher voltage, the PCM thinks the accelerator is depressed and the throttle is open and prevents the shift lock solenoid from energizing (you won’t be able to shift out of Park).

• PCM (Powertrain Control Module)

• Transmission Range Switch


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This is how the Shift Position Interlock works:

Shift Position Interlock
Battery voltage is supplied at all times through under-hood fuse 13 to the brake pedal position switch. With the Ignition Switch in ON (II), battery voltage is supplied through under-dash fuse 21 to the Shift Lock Solenoid. When the Brake Pedal is pressed, a battery voltage input is supplied to the PCM and the MICU. If, at the same time, the accelerator pedal is not pressed, the PCM provides ground to the Shift Lock Solenoid. The solenoid is then energized allowing the Shift Lever to be moved.

 

Texas and Red, thank you for sharing your knowledge.

I want to revise something I said...When I said there was no voltage at solenoid plug, that was not correct. I put my meter on the contacts and saw nothing. By the way you described it, I would not have seen anything as there was no ground connection since that goes through a computer. I never checked from each terminal to ground.

I did put a hitch on this car, but it has about 150 mi of light towing on it. I plan on replacing the fluid once all this is fixed.

Ok, latest update based on what you guys told me: The check engine light has been off for at least 2 weeks and the shifting problems are limited to intermittently not wanting to engage OD completely. Last time I drove it was Tues. Today, daughter gets home from school (she drives it when I don't need it). Said it has been misbehaving the past 2 days. I get in, turn key to run, dash lights up, check engine light goes off after a time. Brake pedal will not release shift lock. Get out, pull TPS plug. Brake will not release shift lock. Start car, get check engine light (as you predicted) but now the shift lock works. Apparently, the fuses and wiring are fine, but the computer is blocking shift lock. Replace TPS plug and take car for drive. Shifts normally up through 4 but will not go to OD, runs about 2500rpm at 55. Can't coax it into OD by accelerating and letting off throttle. Back home with engine still running, pull TPS cable. There is about 4.9v at one pin, the others show no voltage as measured against bare metal on the engine.

It seems odd that with the plug pulled and the computer 'fooled' that the shift lock wouldn't release with the key in run. I know that I've gotten in, turned it to run so that I could put it in neutral to let it roll down the driveway away from the garage.

Another oddity. The lock will work with the plug pulled. If the plug is put back in less than about 5 seconds, the lock doesn't work. If the plug is left off for more than that time, I can plug it back in and the lock works until the car is shut off. When I start it again, the lock doesn't work unless I pull the plug. Don't know if this is significant, but it's repeatable.

If I understand your explanations correctly, this all (at least the shift lock stuff) points to something going on between the signal pin on the TPS plug and the computer, or some computer is messed up. Both could also explain the shifting. You guys have far deeper understanding of it than I do, so maybe you have better idea.

Is there a way to reset PCM without a scanner? That way I don't have to borrow a scanner twice. I can just go and read it next week when I get to town.

Where do I go from here?

Many Thanks
Craig

 

Elevated idle you earlier reported may indicate TPS is not set correctly for idle position or has a fault. Some TPS are adjustable over a narrow range to get acceptable idle position. Shop manual shows TPS as not replaceable and throttle body assy must be replaced to replace TPS, but in some cases I know there are aftermarket TPS part availble.

You need to run through the checks to determine if a fault exists w/ the TPS system. Suggest you purchase a download emanual to guide diagnostics on the TPS system. Try automanualsource.com for a $22 manual.

good luck

 

There are aftermarket TPS available.

Depending on whether the TPS is faulty or not, you may be able to adjust the TPS with instructions that are not part of the service manual. People have posted instructions on the internet on how to adjust Honda's TPS.

 

I'll try it. Pretty inexpensive if it works

Thank You