P0157 is a common OBDII code that occurs in the Ford Fiesta, it’s a general code (this means that it has the same meaning for any vehicle).
This code typically indicates that there is an issue with the wiring or harness going to the sensor, or the sensor itself is bad. There are other things that cause P0157 to populate. We’ll cover those below.
- Bank 2 refers to the side of the engine with Cylinder 2 in the firing order.
- Sensor 2 is downstream of the catalytic converter.
Ford Fiesta P0157 Symptoms
Typically, the only symptom of P0157 is going to be the service engine soon light. Sensor 2 is mostly about checking to see that the exhaust has been scrubbed by the catalytic converter. The exception to this is Dodge Vehicles.
Most of the time, it’s not a breakdown risk. But, like anything that causes the service engine soon light to come on it is a good idea to have it fixed as soon as possible.
P0157 Causes: Ford Fiesta
Here are the most common issues that cause the P0157 code in the Ford Fiesta. They are presented in order (somewhat) of most to least likely to cause the problem.
- Bad Oxygen Sensor– The O2 sensor itself is one of the most likely reasons that P0157 is triggering your service engine soon light. Although it is a temptation to replace it right away, it wouldn’t hurt to check out the wiring harness around it beforehand. See directly below. They are relatively affordable at Autozone or Amazon.
- Wiring Harness Issues– The wiring that goes to the front and rear oxygen sensors is susceptible to damage. This is owes to the fact that O2 sensors are under the chassis where they are subject to punishment from road debris, and they are subjected to a lot of exhaust heat. Sensor 2 is right by the Catalytic Converter, which produces a ton of heat. The downstream sensor is especially susceptible to this problem Here’s how to find a short in the wiring harness (Youtube).
- Plugged Catalytic Converter– That catalytic converter can cause the P0157 code to set. If it’s plugged enough, it’ll feel like the engine runs out of power under enough load. This is because the converter can only let a fraction of the amount of exhaust through that it normally can. If it’s not too clogged, you may not yet feel any symptoms, but the code could be a sign of trouble. How to tell if your catalytic converter is bad (2carpos YouTube).
- Damage to the Terminal– The terminal that the oxygen sensor connects to (the plug) is also relatively susceptible to damage. You’ll want to make sure that there is voltage going to it. There’s more on that directly below.
- Wrong O2 Sensor– If you are getting P0157 after having recently replaced your Oxygen sensor, it may be that the replacement is wrong or bad.
Fiesta P0157 Diagnosis
Here is a fantastic video that covers all aspects of diagnosing the P0157 code:
It is possible to diagnose the P0157 with a multimeter. If you use the multimeter, you’ll know whether or not the voltage coming to and from the oxygen sensor is within spec, this can help you determine if it’s your Fiesta’s O2 sensor, or wiring harness that’s the issue.
If you don’t have access to a multimeter, it certainly wouldn’t hurt to check the wiring to between the fuse box and the Oxygen sensor first. If it ends up being a wiring issue, it’ll save you money over buying an unnecessary O2 sensor.
You can also use a voltage test light to determine whether or not the oxygen sensor is getting any voltage at all (they’re about $5 at Walmart). If it’s not getting any voltage, attach the test light to the harness plug and shake the wiring a little bit. If the light comes on, even for a second, you know that you have a short circuit causing the P0157 trouble code.
Conclusion
Good luck finding whatever caused P0157 in your Ford Fiesta. If you have anything that you would like to add, please feel free to leave a comment below.