P0720 is a generic OBD II trouble code, which means that it has the same meaning for your Chevy Express as it would any other vehicle. It indicates that your Express’s OSS (Output Shaft Speed Sensor) is reporting a malfunction. It’s typically caused by a bad OSS, or a wiring problem.
The OSS works by spinning a gear at the end of the transmission. As it spins, the voltage in the OSS changes. This signal is sent to your Express’s ECM, which uses it to determine when and how hard to shift.
P0720 Quick Facts
- Does not affect the way the engine runs
- Typically caused by a bad output shaft sensor
- Can make the transmission shift rough
P0720 Symptoms: Chevy Express
You should notice symptoms when your Express has P0720. Since the code is transmission related, your engine should run fine. The concern will be how the transmission behaves without the signal from the OSS.
Here are the most common P0720 Symptoms:
- Erratic, delayed shifting
- Speedometer and/or cruise control not working
- Service engine light
- Poor Fuel Economy
In very rare cases the vehicle may misfire or even die when stopping.
Chevy Express P0720 Causes
Here are the most common causes of P0720:
Gear Wear at the OSS
Your Express’s OSS works by spinning a gear and converting that motion to a signal that the ECM can use. Some makes and models use a plastic gear. This gear can wear out over time. How was the speedometer before the code was thrown? Was it ever jumpy? Did it seem accurate? That’s a good indication that the OSS gear could have been compromised. If it has been, you’ll need to replace the gear to fix the problem.
Bad OSS
The Output Speed Sensor itself can be bad. This can happen over the life of the vehicle. You’ll need a multimeter to diagnose it.
Here’s a fantastic video on how to diagnose the OSS with a multimeter.
Wiring Issue
Wiring problems can cause P0720. The wiring for the OSS is lower to the ground than a lot of wiring. It also has a further distance to travel to the ECM. With these two factors against it, it’s more common for the OSS to have wiring issues related to it than a lot of other parts of the vehicle. An open/short or bad ground will throw P0720
1. Check the Harness Connection
Take a look at where the wiring harness plugs into the OSS. Is it corrosion free? Was it plugged in tight? If not clean and replace as needed. Wiring harness issues are very common when diagnosing this code.
2. Broken and Damaged Wiring
Look to see if any of the wiring harness has been compromised. You’re looking for wiring that has been burnt or frayed. Anywhere that it gets close to the exhaust is a great place to look.
Transmission Fluid Temp Sensor
In some vehicles, the OSS is connected to the TFT sensor. If there is a problem with the TFT sensor or the voltage coming from it, it’ll affect the OSS. This will throw P0720.
Conclusion: P0720
P0720 is relatively easy to diagnose. Although, it can be a challenge to get to the OSS. Good luck fixing your Chevy Express. If there is anything that you would like to add, please leave a comment below.
See Also: P0700