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Will an Exhaust Leak Throw a Fault Code? (Explained)

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An exhaust leak occurs when gas escapes from a gap, crack, hole, separation, or missing part in an exhaust system and its pipework.

In this article, we’ll see if an exhaust leak can cause an OBD fault code to be triggered and why this may happen.

example of exhaust leak

Can an Exhaust Leak Cause a Fault Code?

Yes, an exhaust leak can cause a fault code to be triggered. Depending on where it’s located and how serious the leak is, it can disrupt the engine’s air/fuel ratio, resulting in the engine running either too lean (excessive air, insufficient fuel) or too rich (excessive fuel, inadequate air).

If the air/fuel ratio is too lean or rich it can cause a fault code, as the engine’s computer is designed to identify deviations from the standard air/fuel ratio.

Beyond its impact on the air/fuel ratio, an exhaust leak can also cause engine performance issues, potentially setting off an OBD fault code.

However, the presence of an exhaust leak by itself might not always trigger a diagnostic trouble code, or it may be intermittent (turning on and off seemingly randomly).

car OBD scanner

Can It Cause an O2 Sensor Code?

An exhaust leak also has the potential to trigger an error code related to the oxygen (O2) sensor, given that the leak can compromise the precision of the O2 sensor’s measurements.

The role of the O2 sensor entails monitoring the air/fuel ratio within the exhaust gases and conveying this data to the ECU.

Should an exhaust leak result in the engine running either lean or rich, the O2 sensor could identify this and trigger an error code.

However, an exhaust leak might not always be sufficient to initiate an O2 sensor code, or it could be an intermittent issue.

Other issues, such as a faulty O2 sensor or issues within the engine’s fuel system, can also lead to the occurrence of these codes.

Can a Leaking Exhaust Throw a Lean Code?

An exhaust leak can also cause a lean code, as it impacts the engine’s air/fuel ratio it can cause the engine to operate in a lean state (with an excess of air and insufficient fuel).

This can prompt a lean error code, as the ECU identifies the deviation of the air/fuel ratio from the norm.

However, issues beyond an exhaust leak can also bring about a lean code.

For instance, a malfunctioning fuel pump or fuel injectors, as well as issues within the intake system, can contribute to the occurrence of a lean code.


An exhaust leak can throw a fault code depending on the location and severity of the leak and how it affects the engine’s operation.

It can affect the air/fuel ratio and this is why it may trigger the OBD system to store a code.

If you suspect that you have an exhaust leak, it’s important to fix it as soon as possible.

  • Andy Lewin

    Andy Lewin is a senior mechanic, ASE qualified master technician, and an experienced automotive engineer.He's passionate about serving the automotive community with the highest-quality and trustworthy information on all things automotive. He loves to write about car repairs, maintenance, car modifications and tuning, faults, and much more.

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