99 Hyundai slips in overdrive only

Tiny
MJEDLIN
  • MEMBER
  • 1999 HYUNDAI ELANTRA
  • 75 MILES
I have a '99 Hyundai Elantra with a 1.8L engine and automatic transmission. The car tries to shift into overdrive and slips the majority of the time. I have noticed that when it DOES shift into overdrive, that letting up off the throttle causes it to slip out again.

I took it to a transmission shop and paid them to diagnose it, and they told me that they confirmed the computer is sending the signal to shift, so it is an internal problem. I just changed the oil and filter for the transmission and it appears to have helped but only a little, overdrive still slips out more than 50% of the time. Also, the check engine light came on. I'm going to scan the check engine codes tomorrow but I'm not sure how this would have anything to do with the transmission.

Thanks
-Matt
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Monday, October 3rd, 2011 AT 5:26 AM

9 Replies

Tiny
RIVERMIKERAT
  • MEMBER
It could be transmission codes. It could be the shift lock solenoid or control module. If there is a cable from the throttle assembly to the transmission, check the bushings for excessive play.
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Monday, October 3rd, 2011 AT 7:42 AM
Tiny
MJEDLIN
  • MEMBER
Thank you for your reply. I scanned the codes today and this is what I came up with:

P1624: MIL request on signal
P0722: Output shaft speed sensor circuit no signal
P0734: Gear 4 Incorrect Ratio.

I know what the last two mean, and I'm assuming that these two codes are a result of the overdrive problem and not the cause. I have to look up the first one. I will investigate the shift lock solenoid and the control module.

Thanks
-Matt
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Monday, October 3rd, 2011 AT 5:31 PM
Tiny
RIVERMIKERAT
  • MEMBER
From what I can determine, the P1624 code has something to do with the cooling fan circuit.
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Wednesday, October 5th, 2011 AT 3:44 AM
Tiny
MJEDLIN
  • MEMBER
Well according to hmaservice. Com, the hyundai service website, P1624 is a code for the cooling fan circuit for all models except the elantra. On the elantra, it simply means the check engine light is on.

However, P0722 is a signal for "Pulse Generator B no signal."

So I ordered a new set of pulse generators from Hyundai. I read through the service bulletins for my year and model on hmaservice. Com. There is one or two bulletins that deal with the pulse generators. One says that P0722 could trigger P0734 even if nothing's physically wrong with the transmission. However, this bulletin does not address my issue (no 4th gear, slipping into neutral) directly. And because the CEL went off today, I am nervous that the bad 4th gear triggered a no signal for the pulse generator, and not the other way around.

-Matt
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Wednesday, October 5th, 2011 AT 9:12 PM
Tiny
RIVERMIKERAT
  • MEMBER
Hey Matt,

I would trust the information that comes directly from Hyundai, as it should be more accurate and more up to date. I'm sorry that the information I was given to pass on was incorrect. Unfortunately, I don't have access the Hyundai Tech Bulletins as I no longer work directly in the automotive repair industry.
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Wednesday, October 5th, 2011 AT 9:37 PM
Tiny
MJEDLIN
  • MEMBER
Rivermakerat,

thanks for all of your help. I don't expect you to go out of your way, but fyi the hmaservice. Com website is free to use. I pulled up that TSB again and the description states:

description:

The following conditions may be caused by an improperly functioning pulse generator. The conditions may be intermittent and difficult to duplicate.

Delayed or erratic 1-2 shift, with engine hot or cold
Harsh 1-2 shift
Harsh 1-2 downshift, at a higher speed than the normally scheduled downshift
Erratic downshift during light acceleration
Third-gear "Fail-Safe" condition and/or "Check Engine" light on
Vehicle "Bucking and/or Hesitation"

None of which accurately describe my symptoms. So I'm worried that an internal transmission problem triggered the CEL and the codes rather than the codes providing an accurate diagnosis. I think this is reinforced by the fact that turning overdrive off per the OD switch made the CEL shut off after a couple of days.

Thanks again!
-Matt
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Thursday, October 6th, 2011 AT 2:07 AM
Tiny
RIVERMIKERAT
  • MEMBER
I appreciate the info. I'll go and create an account shortly. You may be right. Regular transmissions utilize a linkage from the throttle to the transmission to cause the automatic transmission to shift into and out of overdrive. The switch murkies up the water a bit, though.

Do you have an Aamco near you? They advertise free electronic transmission diagnosis.
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Thursday, October 6th, 2011 AT 4:30 AM
Tiny
MJEDLIN
  • MEMBER
Well, I took it to a local transmission shop a couple of weeks ago that was recommended by my parts guy at NAPA. They only charged me something like $50 but they said it was an internal issue, because the computer was sending the correct signal to shift the transmission into overdrive.

I'm just trying to double check their diagnosis. I can go pull a used transmission at the junkyard for $50 but swapping it in will be a good deal of work.

Thanks for all the help.

-Matt
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Thursday, October 6th, 2011 AT 4:51 AM
Tiny
RIVERMIKERAT
  • MEMBER
Yes it will. It definitely does sound like they're right, though.
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Thursday, October 6th, 2011 AT 6:25 AM

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