98 Millenia 2.5 Speed Sensor & Hold Light - Mazda Forum - Mazda Enthusiast Forums

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Old 08-12-2006, 02:47 PM
Join Date: Aug 2006
Posts: 13
Default 98 Millenia 2.5 Speed Sensor & Hold Light

I have been reading several other forums and I have found that this one has been the most informative about the Millenia’s.

I just purchased a black 98 Millenia 2.5 base model with 85,000 miles. The car runs great, and has a very comfortable ride. With all used car you can always expect to find something wrong with them.

My CEL has been on since I got the car from a private seller. I have always been mechanically inclined and I have always done my own work within reason. So I figured that there would be some bad sensors that needed to be replaced. After checking the OBDII codes, I got a misfire that has been corrected, a knock sensor that will be changed soon, and a P0715 (turbine/input speed sensor circuit). This is where I would need some confirmation as to what to do.

CEL is on now only for the P0715. My instrument panel seems to be working properly. The transmission has been flushed and the ATF level is correct. The transmission does have a rough shift from 1st to 2nd until the car has been driven and warmed up and seems to not shift correctly when you slow down for a turn and then accelerate. The Hold Light comes on from time to time, but turns off once I stop and go again and the Hold Light stays off for the duration of the day.

By what I have read on this forum and on others, it seems to be the speed sensor on the transmission that needs to be replaced. But my concern is; is there a communications problem between the ECM and the sensor. I read in another forum that the wire harness that carries all the communication to and from the ECM is located under the floorboard on the passenger side under the dash and that the connectors go-bad. Is this statement correct and if so could there be a problem in the harness? Will changing the Speed Sensor correct the problem with the transmission or should I check the wire harness?

If babyhuey or anyone can help me correct this issue, it would be great appreciated.
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Old 08-14-2006, 09:26 PM
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Join Date: Jul 2005
Posts: 2,747
Default RE: 98 Millenia 2.5 Speed Sensor & Hold Light

Is never a bad idea to check the wires between the sensor and control module but usually do this after checking the sensor itself. There are no connectors in the harness between the turbine speed sensor and ECM anyway so would have to be a broken wire or bad connection at either end. Check the resistance of the sensor as a first check. The sensor is on the top of the transmission about as far to the end or left side of transmission as you can go. Will probably need to remove the air cleaner housing and battery to get to it but might even be access thru the wheel well opening. It is a two wire sensor with one wire being Red and other being White. Drawing below shows checking resistance so might also get idea of location from that. The sensor should have a resistance of between 253 and 604 ohms. The warmer the transmission fluid is the higher the reading will be.

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Old 08-26-2006, 05:39 PM
Join Date: Aug 2006
Posts: 13
Default RE: 98 Millenia 2.5 Speed Sensor & Hold Light

Thanks for the info. The sensor has no resistence at all. It is completly open. I'll get back to the forum with the result of the replacement soon.
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Old 10-03-2006, 01:44 PM
Join Date: Aug 2006
Posts: 13
Default RE: 98 Millenia 2.5 Speed Sensor & Hold Light

Sorry I took long to return. The turbine sensor has been replaced and the delay in the shifts when slowing down for a turn has improved. The Knock sensor is still pending, but I have started using high octane fuel (93) and my CEL has not come on again. I'll give it some more time to see if it happens again.

The original owner had the tranny flushed but the filter has not been changed. When the car is cold my shifts are a little bit rough until the tranny is hot and the shifts become much smother. Would this indicate that the filter needs to be replaced, and if so would this be an easy job for be to handle. The dealer said that the filter is up inside the tranny and not easy to remove. Is the dealer lying to me again?

Also, I tried a product called Sea Foam that was recommended to me to remove carbon deposits in the combustion chambers and the exhaust valves. I should have asked in the forum first, but I tried it any way. My RPM's have dropped and the idle is also smother. The response to acceleration has also improved some. The engine is running much better than before. Now my concern is, can this product cause any future problems?


This is the link for this product, please let me know what you think. I was going to try it on my Ford Expedition.
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Old 07-10-2007, 07:56 PM
Join Date: Jul 2007
Posts: 1
Default RE: 98 Millenia 2.5 Speed Sensor & Hold Light

hi! we jus t bought a 98 mazda millinia for our daughter and we are having a problem finding a speed sensor we went to get the car inspected and they said the speed sensor was out and needed to be replaced and our local parts store said they do not make them anymore so we are kind of stuck at this point can anyone help us with this situation? maybe know of somewhere online who makes these still
Sherr Robins
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Old 07-11-2007, 11:48 PM
Join Date: Aug 2006
Posts: 13
Default RE: 98 Millenia 2.5 Speed Sensor & Hold Light

Hi SNROBINS. Well i was able to find this part at the Mazda Dealer. But it was a bit expensive. The 2.5 engine was used in several other Mazda models and also in the Ford Probe.I was able to locate some in a local junk yard and tried them out. I found 1 with the same makings as the one in my 98 Milli. After chaging it, the P0719 code has not returned. It was very easy the change, follow babyhuey instruction and go from the top. Thesensoron my Milli was under the engine mount that is visble after removing the battery and tray.

Hope your daughter likes her new ride, mine now has 96000 and is still running great. Some TLC will go a long way.

Babyhuey is a great Mazda mechanic. If you need help this forum has plenty of people that can help.

Let us know how it goes.
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