Transmission Limp Mode

Tony Technician Oceanside, California Posted   Latest  
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Drivetrain
2002 Mitsubishi Lancer ES 2.0L 4-spd (F4A42-1)

Replaced transmission with a used unit due to previous trans. having some slipping issues. This new unit has thrown codes : p0732/p0733/ p0734/p0736 ( gear 2,3,4, and Reverse gear not synchronized)upon first test drive. Scoped input and output speed sensor for any abnormalities and everything looks OK. Rolls well into 2nd & 3rd..but when engaging 4th..it SOMETIMES jerks into 4th then goes into limp mode. Any suggestions you guys might have??

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James Instructor
Jamesburg, New Jersey
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Tony, assuming these are new codes to this trans and you cleared the adaptives before driving...the first thing I would ask is how does it do on a stall test? Is it really slipping?

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Tony Technician
Oceanside, California
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Hey James..tried the stall test. Didnt stall but it sure didnt seem like it was slipping. Motor didnt just (free-wheel)- it had some resistant and car wanted to go. Funny thing about it..its that sometimes it goes through all gears normally and sometimes bangs 3rd really hard and not even tries to go for 4th.

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Zachary Mobile Technician
Austin, Texas
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Good afternoon Tony. Am I correct in assuming that these symptoms are different from the way the original transmission was slipping? I take it both of the speed sensors are a permanent magnet style which generate an ac voltage? I'd do a quick check for AC ripple voltage just to be sure you don't have some kind of noise from the alternator or otherwise giving you weird issues. If you aren't…

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Tony Technician
Oceanside, California
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Hey Zachary. Thanks for replying. One of the things i havent tried yet. Ill give that a try & ill get back to you guys! Thanks.

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Zachary Mobile Technician
Austin, Texas
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No problem Tony. Look forward to hearing how it all shakes out.

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Tony Technician
Oceanside, California
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Performed AC ripple test - not a problem there. Going back to your comment Zachary..the sensors are Hall Effect ( 3 wire). And going back to my captured waveforms...studied the ISS & OSS waveforms a little further & noticed a 326 mv. on the ground side. Sensors get their ground from PCM so thats something ill be looking into. Ill keep you guys updated! �

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Steve Technician
Erie, Pennsylvania
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You had a "bad" transmission. Now you may have two of them. It is also not impossible to swap the input and output sensor connectors. But it is really hard and will do pretty much this. End clutch and housing issues, low/reverse wave spring, TCC engagement issues. There are also several "layers" of limp mode, knowing witch one you are experiencing can be helpful in diagnosis. And lastly, are you…

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Tony Technician
Oceanside, California
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Thanks for your reply Steve. Wiring diagram confirms sensors arent improperly connected. Im starting to think i might have 2 bad trans!..but will continue to do more testing. Made some research before choosing transmission trying to avoid any possible problems. Haha

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Mike Owner
Cromwell, Kentucky
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Can you monitor the gear ratios in each gear with your scan tool? You're going to have to determine is it really slipping or does the tcm just think it's slipping? Will it set the codes on the rack with wheels in the air. If it does, with no load, that could have implications of wrong differential ratio, programming issue, speed sensor issue or?

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Tony Technician
Oceanside, California
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Thanks Mike! Performed stall test & its pretty clear trans is not slipping. As far as the internals - i have no idea if someone has been in there ( although it doesnt show signs of it). Trans was removed from a 2002 Mitsubishi Mirage that showed no signs of vehicle alterations. According to service info - the F4A42-1 all have same gear ratios.

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James Instructor
Jamesburg, New Jersey
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Tony. What Mike is asking is where I was going. If the calculated difference is not within say 200 rpm of actual it will set DTC. Knowing the gear ratio, we can calculate your output speed. The engine will not actually stall during stall test, it has to be in a range according to spec. It is a function of actual engine output (torque) and converter design. If it's too high than the internals are…

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Tony Technician
Oceanside, California
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Makes sense James. The only data I can actually get is ISS counts and OSS counts with TCC slippage % on my scan tool. You guys think that information can be put into an equation to find out "true" values?? I hope Im making myself clear. I'll post a few pictures of the data I recorded while driving to see if we can get something out of it. Appreciate your help James.

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Tony Technician
Oceanside, California
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Here's some data I took while on a test drive. I hope the picture is not to bad. This data (on both captures) is when trans hadn't gone into Limp Mode yet. One capture is when engaging on 3rd gear and before it can shift into 4th..it jerked a little and went into Limp Mode; which put the trans into ONLY 3rd at all times. And the other capture is when transmission finally shifted in 4th gear-held…

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Steve Technician
Erie, Pennsylvania
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Two thoughts on the horizontal oriented picture. 1. AT relay voltage is too low (non existent). This should read battery voltage with the key on, at all times. 2. At an engine speed of 3.3k rpm and the vehicle in third gear, this vehicle should not be able to achieve an actual road speed of 85.13 mph. I would; 1) Verify voltage to the AT relay and two graph ISS, OSS, and VSS before, during and…

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Tony Technician
Oceanside, California
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PCM cuts voltage to A/T relay once it " notices a problem" & its exactly when the trans go into Limp Mode. Once i graphed it...it cuts relay voltage then immediately goes into just 3rd gear. I do have to agree about the MPH Steve. Vehicle never seems to be going as fast as processed data. Trans has no VSS on this year. Would vehicle speed be calculated by the output sensor readings??

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James Instructor
Jamesburg, New Jersey
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Vehicle speed most likely from Rt. Frnt. Wheel speed sensor

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James Instructor
Jamesburg, New Jersey
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I don't like the relay voltage, as Steve has mentioned. It's tough to tell where the PIDs actually come from. I would definately chase the relay voltage first. Stick a meter on it and drive it. With the relay inop you will have 3rd gear. Remove the relay and see what happens...3rd gear.

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Tony Technician
Oceanside, California
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Hey guys! Finally came down to a resolution on this Lancer! Good thing it wasnt customers primary car for transportation so they let us have it for a while. Anyway, after all checks were performed & scoping signals and trying to interpret final synchronized gear ratio from ISS & OSS signals..i decided i had received and installed a 2nd bad unit. So replaced transmission with a third unit…

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James Instructor
Jamesburg, New Jersey
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Good to hear, Tony.

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