Mechanics

TRANSMISSION FLARE

1998 Honda Civic • 4 cylinder FWD Automatic • 164,000 miles

I have a 1998 Honda Civic DX with automatic transmission. When I purchased the car it had a shifting flare from 2nd to 3rd gear. The flare wouldn't occur until the transmission had warmed up by driving and then would persist. The one exception was that with a soft exceleration it would flare, but a hard acceleration it wouldn't flare.
Later I discovered that after some trips of about 75 miles or longer the transmission wouldn't flare anymore no matter how I drove it until after I shut the car off and turned it back on then it returned to flaring again.
I recently changed the transmission fluid and checked all the transmission solenoids for resistances within Honda specs and all activate when energized manually.
The car within the last week had gotten warm while driving so after letting it cool down I replaced the thermostat and bled the system of air.
Now the car's temperature guage fluctuates from normal to hot opperating conditions occaisionally and when it is fluctuating the shifting flare is non existent and when the temperature guage remains at normal position the shifting flare occurs between 2nd and 3rd. Also the left blinker started acting up (first it blinked like a bulb was burnt, then it worked fine, then blinked very slowly and is back to working properly) at the same time that the coolant temperature did. The check engine light is also not on.
The cooling fan works properly and when shorted so fan operates manually it will not cool the coolant temp as indicated by the temperature guage on the cluster.
I took the car to a transmission shop and after investigating it they guessed that one of the "pressure switches" were bad (assuming they were referring to the solenoids). I didn't have them do any further work to the vehicle after that.
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Ihbigred
June 6, 2011.




I have not yet resolved the issue. Here is what I've done since I last updated. Knowing the the engine coolant temperature effected the way the car shifted I troubleshot that area. I purchased a potentiometer that could get down the the range of resistance that the CTS operated in. I found that the CTS was around 200 ohms when car was at operating temperature and that resistance decreased and temperature increased. So I attached the potentiometer to the connector for the CTS and changed the resistance the ECM was receiving to 150 ohms. Wa-Lah! That fixed the problem! Shifted great every time no problems ever. So I figured the CTS was bad. I replaced it and it didn't fix it and I found that the CTSs are not designed to go down to 150 ohms at operating temperature. So I started to lean towards the ECM or shift solenoids again. I stumbled across another used ECM with 215k miles on it and that didn't fix it, so I swaped the AB shift solenoid pack out for another used set, and that didn't make any difference also. Another thing, I've got the other car that is doing the same thing running, the one I converted to V-TEC with non-V-TEC transmission, and it continues to also flare from 2nd to 3rd once warmed up. So I'm still searching and I'm almost positive that it's not an issue internal to the transmission. By the way, what is the purpose and what does the linear shift solenoid do on these cars?


Tiny
Ihbigred
Jan 27, 2012.
I'm not exactly sure what that solenoid does or is for, but I've seen it referred to as the line pressure solenoid. Here's a link I found:
http://techauto.awardspace.com/transmission.html

Also, I didn't re-read the whole thread here. Have you have the trans pressure tested?

I also saw a few places where people have removed and cleaned the solenoids and the problem was cured.


Rivermikerat
Jan 27, 2012.
An update on what I have recently done. Rivermikerat, no I have not checked line pressures as I don't have a gauge for that. I cleaned the solenoid and checked the gasket for cracks and then reinstalled and car continued to flare so I ended up purchasing a Honda OEM linear solenoid to rule that out as the problem. After replacing the car seemed to shift better between all gears but continued to flare worse and worse as the car warmed up. I read a thread that someone had very similar issues to mine and replaced the linear solenoid and that resolved the issue for a few months till the solenoid went out and had to be replaced again for which it only went out again after a year. It was suggested that the PCM might have been bad and in turn causing the solenoid to be ruined over time. I tend to continue to swing towards the PCM being faulty because of being able to trick the PCM into thinking it's running warmer and thus it shifting just fine. What are the output voltages and from what pins on the PCM should I get for the linear solenoid and AB shift solenoids? I think this would be a good test to see what the outputs are to both the linear and AB shift solenoids at the point the car shifts from 2nd to 3rd to see if these are good outputs.


Tiny
Ihbigred
Feb 9, 2012.
Are there any troubles codes now?
What type of transmission fluid was used? Is the fluid level correct?

A scan tool would enble you to monitor voltages. Since problem is not there all the time, only real time data analysis would tell you if there is anything wrong with the voltages.

A partially clogged fluid cooler inside the radiator can cause such problems.


KHLow2008
Feb 9, 2012.
No trouble codes. I took it to a tranny shop earlier on in this discussion and they checked for codes. I used only Honda ATF and fluid level is okay. I just deicded to pull some data with my multi meter from the pinout diagram. Shift solenoid B is at battery voltage till shifting from 2nd to 3rd. The voltage drops off cleanly every time even when it is flaring from 2nd to 3rd. The linear solenoid voltage sits at 1.15V while driving and just before shifting it drops to 0V. I noted when it flares it stays on 0V longer than any of the other shifts. I can't say it does that also when its cold and not flaring. I'm waiting for the car to cool down then I'm gonna go check that out. Maybe a plugged cooler section in the radiator, but that doesn't seem to tie with the ECT being directly related to the shift flare.


Tiny
Ihbigred
Feb 9, 2012.
Most stores like Autozone and Pep Boys will rent (cheaply) or loan transmission fluid pressure gauges that you can use to test with.


Rivermikerat
Feb 9, 2012.
A plugged cooler can affect the transmission fluid temperature and line pressure. The transmission fluid temperature and ECT readings could be confusing the PCM to result in the flaring.
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KHLow2008
Feb 10, 2012.
Rivermikerat, I will see if I can rent one or find someone with one. Also, I've never done that particular test, should I just pick the car up and run it through the gear to see the pressure readings?
KHLow2008, I'll pull the lines and throw some pressure at it to see if anything is getting through.
Last night, I checked some more voltage readings.
B1 - Power supply to linear solenoid negative electrode
B2 - Power supply to linear solenoid positive electrode

I check the voltage difference across B1 and B2 while shifting from 2nd to 3rd with the car warm and it was 1.15V just before shift. When I put the potentiometer in place of the ECT sensor (set at 150 ohms) the voltage difference across B1 & B2 was 1.25V. Seeing that an increase in voltage difference across those two PCM pins created a positive shift from 2nd to 3rd I checked each pins voltage to ground. B1 to ground read at -1.39V then dropped to 0V when shifting to 3rd and car was warm. When I put the potentiometer in place, B1 to ground was about -1.408V then dropped to 0V when shifting to 3rd. B2 to ground read 0.113V then raised to 0.5V when shifting to 3rd with car warm and with potentiometer in place B2 to ground read 0.115V then raised to 0.5V when shifting to 3rd. These readings seem a bit weird because their sums to follow the readings I got earlier when measuring across B1 and B2 but I used a PCM ground wire instead of the body (may be the problem). So it seems from the readings across B1 and B2 that an increased voltage difference across the linear solenoid made the car shift great. So I'm wondering what the linear solenoid really does? I know it only deals with high and low pressure (pretty vague, any help would be appreciated). So maybe by increasing the low pressure side voltage I'm allowing more pressure to build up before it shifts thus creating a better shift? (Trying to follow the flow process attached)


Tiny
Ihbigred
Feb 10, 2012.
Yes. That works. It'll be much easier than trying to do it on the road.


Rivermikerat
Feb 10, 2012.
Greetings ihbigred: I have been following your situation over the last several weeks on this thread. I have a 1996 Civic EX with 102000 miles on it that I purchased recently. The vehicle is exhibiting the exactly same 2nd to 3rd gear shift flare that you describe. Trans shifts fine when cold but when the temp reaches normal, the 2-3 flare will occur and also only under light acceleration.
I have not gone as far as you have in my investigation yet. I have done a 3 x3 drain and refill with Honda's new DW-1 atf and saw no improvement in shift quality. I also removed the lock up, shift and linear solenoids, cleaned them, tested the operation and resistance. All were good and within the OEM specs.
I am posting not because I can offer you any insight but to show my support and to let you know that at least one other person out there has experienced the same issue as you have. I am hoping that you will be able to solve this problem and share your solution with others. Also, I wanted to thank you for all your hard work so far. Please know that what you have shared has helped me also, if for no other reason than to realize that I am not crazy in trying to solve this issue!
By the way, my vehicle has been serviced almost exclusively by a Honda dealership during its lifetime so, the car has been well-maintained.


Tiny
Bgorpy
Feb 12, 2012.

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