What is OBDII - PO715 input/turbine speed sensor circuit malfunction???

[doitmyself]

Hi guys,

This code is showing up on a Ford escort.

What is a "input/turbine speed sensor circuit malfunction" and how do I fix it????

Thanks,

as always, trying to "doitmyself"

 

[Gary Allan]

My manual doesn't have that specific code in it ..but everything around it in # is a trasmission code.

Look for an unplugged/damaged wire would be my first move. There would probably be other codes for "too high" or "too low" (always high or always low) type situations that would indicate a bad sensor. This reports "no signal" I believe.

 

[doitmyself]

Thank you very much Mr. Allan. This might explain the occasional "rough" shift when the check engine light goes on.

I will check the wiring harnesses on the tranny as a start. If that doesn't work, I'll try hitting something with a big hammer.

Best Regards.

 

[1 FMF]

just a guess, if it's a tranmission code then the "input/turbine speed" makes me think of torque converter for an auto, and possibly something to do with tq converter lockup.

 

[Gary Allan]

Yes, 1 FMF, this sensor circuit may be a component of the code that reads input and output speeds to determine if the clutch has engaged. I had thought that it read engine rpms vs. the VSS and merely detected the lack of rpm reduction ..but it may be more sophisticated than that.

 

[brianl703]

Because it says "circuit malfunction" that indicates to me that the problem is a lack of reading...a bad sensor, or a bad connection to the sensor.

Otherwise, the code would say "reads low" or "reads high".

That the problem is intermittent would also indicate that the problem is electrical in nature.

 

[brianl703]

There are OBD-II summaries available for Ford vehicles here:

http://www.motorcraftservice.com/vd..._theory_retail&gutsid=diagsheet&menuIndex1=29

Here is what Ford has to say about this code:

The Vehicle Speed Sensor (VSS), Turbine Shaft Speed (TSS) sensor and Output Shaft Speed (OSS) sensor, if
equipped, are analog inputs that are checked for rationality. If the engine rpm is above the torque converter stall
speed and engine load is high, it can be inferred that the vehicle must be moving. If there is insufficient output from
the VSS sensor, a malfunction is indicated (P0500). If there is insufficient output from the TSS sensor, a
malfunction is indicated (P0715). If there is insufficient output from the OSS sensor, a malfunction is indicated
(P0720).

 

[doitmyself]

Wow, thanks Brian!

"If there is insufficient output from the TSS sensor, a malfuntion is indicated (PO715)".

A malfunction of what? The TSS sensor? Or, could a mechanical malfunction of the tranny cause this sensor to have a poor reading?

Thanks again.

 

[brianl703]

The way I read it, it's saying that the vehicle is moving because engine is above stall speed + engine load is high. Since the vehicle is moving, it should be getting input from the TSS.

Since it is not getting input from the TSS, the computer determines that there is a malfunction with the TSS or it's wiring.

If it were a problem with the transmission--like the transmission were slipping--the engine load would not be high and you would not get this code.


According to the manual:

Typical TSS functional check malfunction thresholds:
vehicle is inferred to be moving with positive driving torque and TSS < 200 rpm for 5 seconds

Just a guess, but I'd expect a whole lot more in the way of symptoms than just a rough shift if the turbine shaft speed really did drop to < 200 RPM. Like major, major transmission slippage.

EDIT: There are separate codes for torque convertor slippage problems.