getting P0640 code??? - Diesel Forum

blandproud · 08-13-2009, 02:12 PM

ok i just got this code 2 times. i figured out if i break torque it a little bit it will throw this code? P0640. its flashing the overdrive light when it trips it. the other day i got a code about the speed sensor or somethin but i had my old computer xle4 in it when it threw that code and the od light started flahing. i can't find any good code list and this is getting the best of me.........the tranny only has 8k on it. if anyone has any ideas please speak before my truck takes a joy ride off a cliff.....

blandproud · 08-13-2009, 02:15 PM

this is what the code is

P0640 Manifold Intake Air Heater

WHY would the trans light be flashin for this code?????????????????

blandproud · 08-13-2009, 03:05 PM

other code was

p0720 OSS Sensor circuit malfunction

od light also flashed on this one

**Flywheel** · 08-13-2009, 04:43 PM

The OD did not flash on the air intake heater code, which has likely been removed, thus the reason for the code.

your VSS issue will trigger the flashing OD light. I would remove and clean the VSS.

YAMAHAMMER · 08-13-2009, 04:54 PM

Sorry, whats the OSS/VSS?

**Flywheel** · 08-13-2009, 04:59 PM

OSS - Output shaft speed sensor
VSS - vehicle speed sensor

so you may need to clean the OSS - not the VSS - do both....

blandproud · 08-13-2009, 06:00 PM

Quote:

Originally Posted by Flywheel

The OD did not flash on the air intake heater code, which has likely been removed, thus the reason for the code.

your VSS issue will trigger the flashing OD light. I would remove and clean the VSS.

i have a early 99 which i believe does not have the intake heater.

Also what do you mean by the OD did not flash on the p0640 code? i can have it in park rev it and it will trip the OD light. ??? i just put in a newer pcm. it was a nvk4 but Jody flashed it to a Pmt1. could this have somethin to do with it? i don't get why it sets off the OD light for this code? only thing i can guess is the newer PCM has somethin to do with it?

Where are these sensores located ?

tbpower · 08-13-2009, 06:29 PM

The code 640 is going to show up anytime you read the codes so don't necessarily link it with the overdrive flashing. If you have a newer computer it is going to be looking for the air intake heater that you said you don't have. The vss is on the rear differential on top of the "pumpkin".

tbpower · 08-13-2009, 06:53 PM

The oss is on the top rear of the tranny.

blandproud · 08-13-2009, 10:33 PM

so what should i do about the OD light? truck shifts fine and the OD light don't come on while driven either?? i am using a SCT to pull the codes. anybody have any advice?

tbpower · 08-13-2009, 10:39 PM

Quote:

Originally Posted by Flywheel

OSS - Output shaft speed sensor
VSS - vehicle speed sensor

so you may need to clean the OSS - not the VSS - do both....

I think I would go with the oss first and go from there.

MilitiaAir · 08-13-2009, 11:43 PM

I would clean the sensors and see if help. It might have something to do with the new PCM tho.

blandproud · 08-14-2009, 10:32 AM

it just worries me cause it did it with the old pcm at first. i do have warrenty on tranny but i don't want to deal with the guy that built it cause he prob doesn't want to see my truck again after how long it was in the shop lol

blandproud · 08-14-2009, 02:23 PM

hmmm i just got back from tranny shop..no codes present for the tranny. i also pulled the dp before i went over there. i could trip the od light when i had the dp in by barely giving it gas while on the break. i also pulled the plug off and reconected it, but i still got the od light after that....but now with the dp off it wont do it? i got over there told him what to do and bam nothin worked fine. ....so i still have dp off and MIGHT reconnect it and see if it happens but i don't know.....

TransBrain · 08-15-2009, 11:10 AM

It sounds like the parameters for the output speed sensor circuit are corrupted with the tune or there may be some wierd electrical noise the tune is picking up.

When you're in Park, and you rev the engine, the output shaft which is what the OSS is reading should be zero. If it sets an OSS code in this situation, then the PCM is detecting a circiut problem or actual movement of the output shaft which we know is impossible. I have run into electrical noise problems in these type of situations and have installed noise suppression filters to get rid of them, however this kind of sounds like a tune, possible sensitivity issue. I'd still check

If you can monitor the output shaft speed data with your scan tool, try running your tune again to diagnois what the PCM is seeing. This is not an internal trans issue so your trans tech should be okay. It might be a good idea to let him know about the particulars in your case (the tune) so if a future problem were to arise, you/he aren't chasing your tail.

The guys are correct, the PO 640 will not cause trans limp mode