What is OBD-II Code P0099 – Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic Bank 1

Diagnostic trouble codes (DTCs) are valuable tools that allow mechanics to identify and repair issues in a vehicle’s engine. One of the codes that can occur is OBD-II Code P0099 – Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic Bank 1. This code can appear in a wide range of vehicles, and it’s important for drivers to understand what it means and how it can be fixed. In this article, we’ll explore what this code indicates, how it can be diagnosed, and what repairs may be needed to resolve the issue.

What is OBD-II Code P0099?

OBD-II Code P0099 refers to an issue with the circuit that monitors the intake air temperature (IAT) sensor. Specifically, this code indicates that the circuit related to the second bank of cylinders is experiencing intermittent or erratic issues. The IAT sensor is a critical component of the engine control system, as it helps regulate the amount of fuel that is injected into the engine based on the temperature of the air that is being pulled in.

When the engine control module (ECM) detects that there is an issue with the IAT sensor circuit on the second bank of cylinders, it sets a Diagnostic Trouble Code (DTC) and illuminates the check engine light on the dashboard. In many cases, the engine may still run, but it may not operate as efficiently as it should.

Diagnosing OBD-II Code P0099

Diagnosing OBD-II Code P0099 begins with connecting a scan tool to the vehicle’s OBD-II port. Once the tool is connected, the mechanic can read the DTC and determine what diagnostic steps need to be taken. The first step is often to verify that the check engine light is actually illuminated and that the code that is being reported is accurate. If multiple codes are being reported, it’s important to address them in the order that they appear.

Next, the mechanic will inspect the IAT sensor and the associated wiring and connectors. The IAT sensor is usually located near the air filter box, and it may be located on the intake manifold in some vehicles. The mechanic will look for signs of damage or wear, such as broken wires or corroded connectors. If any issues are found, the mechanic will replace or repair the affected components as needed.

If the IAT sensor and the associated wiring and connectors appear to be in good condition, the mechanic will move on to testing the resistance and voltage of the circuit. This can be done using a multimeter, and the mechanic will consult the vehicle’s service manual for the specific resistance and voltage values that are expected for the circuit. Any values that fall outside of the expected range may indicate a problem with the circuit that needs to be addressed.

Finally, if all of the above steps have been taken and no issues have been identified, the mechanic may choose to replace the IAT sensor itself. This is often a last resort, as the sensor is a relatively expensive component and it may not be the root cause of the issue. However, if all other diagnostics have been exhausted and the IAT sensor is the only remaining suspect, it may be worth replacing it to see if it resolves the issue.

Repairing OBD-II Code P0099

The specific repairs needed to address OBD-II Code P0099 will depend on what the diagnostic process has revealed. In some cases, simply repairing a damaged wire or connector may be enough to solve the problem. However, in other cases, more extensive repairs may be needed, such as replacing the IAT sensor or even replacing the ECM itself.

One thing to keep in mind is that intermittent issues can be difficult to diagnose and repair. If the issue only appears intermittently, it may be challenging to identify and fix the underlying problem. In some cases, the mechanic may need to wait for the issue to become more consistent before they can properly diagnose and repair it.

Frequently Asked Questions

1. What are the symptoms of OBD-II Code P0099?
The most common symptom associated with OBD-II Code P0099 is an illuminated check engine light. In some cases, the engine may run roughly or operate less efficiently than it should. Other symptoms may include a decrease in fuel economy, decreased engine power, or the inability to pass emissions tests.

2. Can I drive my vehicle with OBD-II Code P0099?
It is generally safe to drive your vehicle with OBD-II Code P0099, although you may notice a decrease in fuel economy or engine performance. However, it’s important to have the issue addressed as soon as possible to prevent further damage to your vehicle and to ensure that it is operating safely.

3. How much does it cost to repair OBD-II Code P0099?
The cost to repair OBD-II Code P0099 will depend on what is causing the issue. In many cases, simply repairing a damaged wire or connector may be relatively inexpensive. However, if more extensive repairs are needed or if the ECM itself needs to be replaced, the costs can quickly add up. It’s always a good idea to get a quote from a reputable mechanic before authorizing any repairs.

4. Can I diagnose OBD-II Code P0099 myself?
While it may be possible to diagnose OBD-II Code P0099 yourself using a scan tool, it’s important to understand the diagnostic process and to have the appropriate tools and knowledge to make accurate diagnoses. If you’re not confident in your ability to diagnose and repair engine issues, it’s best to take your vehicle to a reputable mechanic for professional assistance.

5. How can I prevent OBD-II Code P0099 from occurring in the future?
The best way to prevent OBD-II Code P0099 from occurring in the future is to perform regular maintenance on your vehicle. This includes regular oil changes, air filter replacements, and other necessary maintenance tasks. Additionally, being aware of any changes in your vehicle’s performance or operation and addressing issues as soon as they arise can help prevent more serious problems from developing.


OBD-II Code P0099 is an issue with the circuit that monitors the intake air temperature sensor on the second bank of cylinders. Diagnosing and repairing this issue can be challenging, as many different components may be involved. However, by following the diagnostic process outlined in this article and working with a reputable mechanic, drivers can get their vehicles back on the road safely and efficiently. Remember to always address check engine lights promptly to prevent further issues from developing.

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