P0660 is a somewhat common OBDII code. It’s generic, so it has the same meaning for the GMC Sierra as it would any other vehicle made for the 1996 model year and up.
This code indicates that there is an issue with the bank 1 side of the intake manifold valve tuning control circuit. Common causes for P0660 include a bad wiring harness to/from the intake tuning valve, a bad PCM, or a bad intake manifold tuning valve control circuit. It’s most commonly caused by wiring issues.
P0660 Definition: Intake Manifold Tuning Valve Control Circuit Open (Bank 1)
Here’s the meaning of the P0660 definition divided into its three distinct parts.
Intake Manifold Tuning Valve Control Circuit
The intake manifold tuning valve control system is responsible for redirecting air inside your Sierra’s intake manifold.
It relieves air pressure on the opposite side of the intake manifold. Or, it can channel air down a completely different runner for power/efficiency purposes.
Open
An open implies that two points of an electrical circuit are externally disconnected. In this case, the two points in question are the PCM and the intake manifold tuning valve control circuit.
The wiring between these two parts of your Sierra may run through the CAN bus system, which is a wiring junction. Getting a schematic for your vehicle (the exact model year and engine combination is essential) can make determining the cause of P0660 much easier. You should do a quick visual inspection for obvious issues before doing so (more on that below).
Any one of your Sierra’s modules can detect this issue. Examples of different modules include body control, transmission, ABS, traction control. If there’s a PCM issue, the other modules can still report P0660.
Bank 1
Bank 1 is the part of your vehicle with the first cylinder. You don’t need to concern yourself with this if you have an inline four-cylinder engine or inline-six.
P0660 Symptoms: GMC Sierra
There usually are symptoms associated with P0660. Here are the most common ones:
- Check engine light
- Decreased power at the higher end of the RPM range
- Decreased fuel mileage
- Rough/choppy idle
- Difficulty starting
It’s more likely that the decreased engine power will be at the higher end of the RPM range. It can happen at any engine speed. You may only notice the check engine light.
GMC Sierra P0660 Causes and Diagnostics
Here are the most common causes of P0660 and a good order to diagnose your GMC Sierra in at home.
1. Check for Manufacturers Communications
Manufacturers (including GMC) send communications via “technical service bulletin,” commonly referred to as TSB’s. While this site doesn’t keep a database of them, they are easy to find online.
If you click on the link above, it’ll take you to the NHTSA website in a new window. Look for your exact year and engine combination GMC Sierra on there. If there is a TSB related to the intake manifold tuning valve, it gives you a great place to start your diagnosis with a known point of failure.
2. Inspect the Wiring Harness
Check the wiring connector on the bank one side of the intake manifold tuning valve control circuit.
Examine where it plugs into the harness. Make sure that there is no visible damage to it or the pins inside. If there is damage, you may need to repin or replace it. If there is corrosion, use a good electrical contact cleaner to clean it.
Now that you’ve established that the harness connector looks good, examine the wiring coming from the intake manifold control valve as far as you can. Look for damaged, frayed, or burnt wiring. If there is, replace the wiring in question.
Verify that the ground wire is solid and free of corrosion where it bolts to the body, engine, or frame. Then, run a temporary ground to the intake manifold tuning control valve. If it solves the problem, you’ll need to fix your Sierra’s OEM ground wire.
3. Bad CAN Bus
The CAN bus is responsible for taking information from the various sensors and sending it to whatever modules need it (including the PCM).
If the wiring harness seems fine until it reaches the CAN bus system, its pins will need to be inspected, which is getting into the weeds for most shade tree mechanics.
A mechanic would be able to use a specialized scanner to determine precisely where in the wiring system the wiring harness is open and causing P0660 in your Sierra. They could also check the continuity of the circuits.
4. Other Causes
- Bad PCM/ECM- While the PCM is rarely the problem with most codes. If everything checked out with the wiring, replacing or reflashing the PCM can clear P0660. Have a mechanic take a look at your Sierra before replacing a PCM.
- Bad Intake Manifold Tuning Valve- P0660 indicates a wiring issue with the intake manifold tuning valve. But, if its wiring can fail internally, which will throw the code. It’s not very high on the probability scale.
Conclusion
It can be difficult to chase down some of the wiring issues that can cause P0660 in the GMC Sierra. But, it’ll often be caused by something that is easy to see under the engine bay. There’s nothing wrong with having a look. Good luck!