So your check engine light is on. As you probably know, the check engine light (CEL) can light up for all sorts of reasons. But since the introduction of OBD-II back in the 1990s, many of those reasons are stored in a standardized set of diagnostic trouble codes that can be accessed with a generic code reader.
The good thing about the CEL and the entire OBD-II engine management and diagnostic system is that it takes a lot of the guesswork out of what's actually going on with a vehicle's engine and drivetrain. A tech can connect a code reader to the OBD-II port and quickly access any trouble codes that are stored in the engine computer, pointing him or her in the right direction for diagnosis and repair.
NOTE: Code scanning is one of the free services available at your local Advance Auto Parts store.
Where it can get tricky, though, is interpreting what the trouble codes mean. At times, there's a certain amount of reading between the lines needed to come up with an informed conclusion on why a certain code might be stored—and a single problem might cause a cascade of trouble codes to all be stored.
To help you learn more about these codes and decide whether the issue is one you can tackle yourself or one that you should take to a trained technician, Advance Auto Parts will be breaking down common codes. In this article, we focus on trouble code P0715 and what it means.
P0715: Input/Turbine Speed Sensor Circuit Malfunction — What It Means
Your vehicle's automatic transmission is one of the most complex systems in the whole vehicle, and one of the most expensive to repair if something goes wrong. The good news is that transmissions are more efficient and reliable than they've ever been, and it's not unusual for a vehicle to pass the 200k mile mark without needing a transmission rebuild.
Your transmission's job is to transmit the engine's power to the wheels. As part of its normal operation, the transmission optimizes engine RPMs to a desired speed by adjusting gear ratios. On a modern transmission, it relies on an input speed sensor to inform the powertrain control module (PCM) of engine RPMs.
The P0715 code means there's a disconnect between the information from the input speed sensor and transmission control module (TCM) vs. what the PCM is receiving. In an instance like this, the PCM can't dictate shift points according to manufacturer's specs.
Symptoms
- Hard or erratic shifting
- "Gear hunting"
- Failure to shift at all
- Vehicle in "limp-in" mode with a top speed of around 35 mph
- In rare cases, no symptoms
What Happens If I Ignore It?
As mentioned above, some vehicles might not show any symptoms at all other than an illuminated check engine light. In other cases, the transmission just won't shift out of first or second, or the vehicle might be in limp-in mode and limited to about 35 mph. Obviously, any of these scenarios is not good.
Possible Fixes
A P0715 code can be caused by a failed transmission valve body, dirty transmission fluid or a low fluid level, problems with the shift solenoids, or damaged or corroded speed sensor wiring or connectors. These problems, however, might also register other trouble codes along with P0715.
In most cases, a P0715 code will be the result of a failed or defective input speed sensor.
A technician will first examine the speed sensor and its wiring, and use a multimeter to check the sensor's ground and voltage specs. The sensor can then be replaced and the TCM and PCM reset to clear the code. If that doesn't take care of the problem, chances are there may be an internal issue with the unit that should be addressed by a transmission shop.
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About the Author(s)
Jerry Renshaw is a veteran journalist, gearhead and guitar player, and cultivated his mechanical skills by 30 years of turning wrenches to keep one piece of junk or another on the road. He's owned everything from a Chevette to (three) minivans to a fire-breathing Dodge muscle truck, and is constantly keeping up to speed on what's going on in the automotive world.
