Technical Description of OBD-II Trouble Code
The circuit controlling the deactivation and intake valve of cylinder 12 is experiencing low voltage or resistance.
What does that mean?
This is a generic powertrain diagnostic trouble code (DTC) that can be found in many OBD-II vehicles (1996-newer), including those from General Motors, Dodge, Jeep, Chevrolet, Chrysler, Ram, and others. The exact repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
OBD-II trouble code P3491, along with related codes P3489, P3490, and P3492, are associated with the control circuit for cylinder #12 deactivation and intake valve.
The purpose of the cylinder 12 deactivation/intake valve control circuit is to enable the cylinder deactivation feature, such as the V4 mode of a V8 engine, which improves fuel economy during light load operation, such as highway driving. The Engine Control Module (ECM) controls the engine’s 4 or 8 cylinder modes by engaging the intake deactivating solenoids for four of the engine cylinders. This code specifically pertains to the number 12 cylinder, while the other three cylinders involved in this process are determined by the engine configuration and firing order. The number one cylinder deactivation solenoid is located near the intake of that cylinder, depending on the specific vehicle and configuration.
When the ECM detects voltage or resistance within the cylinder 12 deactivation/intake valve control circuit that is too low, below the normal range threshold, it sets code P3491 and may illuminate the check engine light, service engine soon light, or both. In some cases, the ECM may disable the injector to the #12 cylinder until the issue is resolved and the code is cleared, resulting in a noticeable engine misfire.
Cylinder deactivation solenoids:
What is the severity of this DTC?
The severity of this code can range from moderate to severe, depending on the specific symptoms of the malfunction. A misfire should be addressed immediately, as it can cause permanent damage to internal engine components.
What are some of the symptoms of the code?
Symptoms of a P3491 trouble code may include:
What are some of the common causes of the code?
Causes for this P3491 code may include:
What are some P3491 troubleshooting steps?
The first step in troubleshooting any malfunction is to research the Technical Service Bulletins (TSB’s) for the specific vehicle, based on the year, model, and engine. This can save time by providing guidance in the right direction.
The second step is to check the engine oil level and ensure it is at the appropriate level. Then, inspect all components associated with the cylinder 12 deactivation intake valve control circuit for any visible physical damage. Depending on the specific vehicle, this circuit may include several components, such as the deactivation solenoid, switches, fault indicators, and the ECM. Conduct a thorough visual inspection of the wiring associated with these components, looking for any obvious defects like scraping, rubbing, bare wires, or burn spots. Next, check the connectors and connections for security, corrosion, and damaged pins. This inspection should cover all wiring connectors and connections, including those to the ECM. Consult the specific technical data for the vehicle to verify the configuration of the cylinder 12 deactivation/intake valve control circuit and confirm every component incorporated within the circuit, which may include a fuse or a fuse-able link.
Advanced Steps
The advanced steps are highly specific to the vehicle and require advanced equipment for accurate performance. These procedures involve using a digital multimeter and referencing the specific technical information for the vehicle.
Voltage Checks
The reference voltage and acceptable ranges may vary depending on the specific vehicle and circuit configuration. The technical data will include troubleshooting charts and the appropriate sequence to follow for an accurate diagnosis.
If this process reveals a lack of power source or ground, continuity testing may be necessary to check the integrity of the wiring, connectors, and other components. Continuity tests should always be performed with the power removed from the circuit, and normal readings for wiring and connections should show 0 ohms of resistance. Resistance or lack of continuity indicates faulty wiring that is open, shorted, or corroded, and it must be repaired or replaced.
What are some common repairs for this code?
Common Mistake
We always recommend seeking professional service to resolve this issue. However, if that is not possible, we offer the option to permanently delete this specific DTC. All other codes will continue to be addressed. If you are interested in this option, please upload your ECU file to our portal.
