P2006 is a general diagnostic code. It is applicable to all vehicles made after the 1996 model year, including the GMC Sierra.
The most common causes of P2006 are wiring problems with IMRC Actuator, carbon deposits on the IMRC butterfly flaps, or a bad intake manifold runner position sensor.
P2006 Definition: IMRC – Stuck Closed – Bank 1
Here is the definition of P2006. Understanding it can help make diagnosis easier.
IMRC Control
Your GMC Sierra’s throttle body allows air into the intake manifold. Once the air makes its way through the intake, the IMRC fine-tunes the airflow for each particular intake runner. This action creates a swirling effect that allows for more efficient combustion.
The IMRC is controlled by your Sierra’s powertrain control module (PCM). It can use either engine vacuum or an electric motor to operate the system (depending on model year and engine type). However, the vacuum-operated version does seem to be more prevalent.
Stuck Closed
The IMRC is stuck closed and can no longer fine-tune the air. If it is stuck closed, it can limit air intake at higher RPMs. This may cause some unwanted effects (covered below).
Bank 1
Each of your Sierra’s cylinder heads is considered to be a “Bank.” Bank 1 is the cylinder head with the first cylinder. You don’t need to worry about this at all if your vehicle has an inline engine, as there is only one bank of cylinders.
On bank 1, the code is P2006. If bank 2 were stuck closed, the code would be P2007. If the IMRC was stuck open, the code would be P2004.
P2006 Symptoms: GMC Sierra
Here are the most common symptoms associated with P2006:
- Rich air/fuel mixture
- Decreased fuel economy
- Surging Engine/Stalling
GMC Sierra P2006 Causes + Diagnosis
Here are things most likely to cause P2006 in your Sierra, as well as a good order to look at them in:
1. IMRC Wiring
The wiring harness going to the IMRC and the pigtail that connects to it can cause P2006. If the IMRC actuator no longer has power, then it can’t operate the butterfly valves.
Check the wiring harness around your Sierra’s IMRC to ensure that it hasn’t been rubbed against anything and damaged. If it has, you’re going to need to replace or repair the wiring harness.
Make sure that the harness has the proper voltage (or voltage going to it at all). Verify that the ground is good.
2. Restricted Vacuum Lines (Vacuum Operated IMRC Only)
Most IMRC systems are vacuum controlled. Check the vacuum lines going to it to see if they are restricted or damaged in any way. If there is a leak, you’ll need to replace the lines.
If your Sierra has a vacuum-operated IMRC, you can control the butterfly valves with a vacuum pump (like a Mityvac). Use a vacuum pump to verify that the IMRC actuator can still operate the butterflies. If it does operate them, you know that either there’s not enough vacuum getting to the IMRC actuator for it to be effective, or something is not commanding it to turn on.
If the vacuum pump does not operate the IMRC actuator, it’s likely bad and causing P2006.
3. Intake Manifold and Linkage
With your Sierra’s IMRC actuator disconnected, you can operate the linkage by hand. It shouldn’t give any resistance when moving it. If it does, then it’s binding in the intake. This can happen for a few reasons:
- Carbon build-up
- Intake manifold improperly torqued
- Bent or loose IMRC butterfly valves
If the butterfly valves open and close with no resistance, you can rule out any issue with the intake, which either leaves the IMRC actuator or something causing it not to command open or closed.
If they do not freely move, there is either a carbon buildup or the butterfly valves have come loose.
4. Bad MAP/MAF Sensor
The PCM uses data from your Sierra’s manifold absolute pressure (MAP) or mass airflow (MAP) sensors to verify that the butterfly valves have opened as much as they should have (or at all).
If it does not see the data that it should, that can be enough to throw P2006.
5. Bad IMRC Actuator
Replacing the IMRC actuator is the most common fix for P2006. In the previous step, you checked all of the wiring going to it and ensured that it was good. So, at this point, it’s likely to be the IMRC actuator causing P2006.
Conclusion
As you can see, there are a lot of potential causes of P2006. The good news is that most of them are easy to test. Good luck repairing your Sierra.