P2021 – Intake manifold air control actuator position sensor/switch, bank 2 – circuit low

By Reinier (Contact Me)
Last Updated 2017-01-12
Automobile Repair Shop Owner

Table of Contents

1. What Does Code P2021 Mean?
2. What are the common causes of code P2021?
3. What are the symptoms of code P2021?
4. How do you troubleshoot code P2021?
5. Get Help with P2021

What Does Code P2021 Mean?

SPECIAL NOTES: Due to the vast number of different manifold air control system designs in use today, non-professional mechanics are strongly urged to read the section in the manual for the application being worked on that deals with this system before attempting a diagnosis of code P2021, or any of its related codes, these codes being P2019, P2020, P2022, and P2023.

Failure to gain at least a basic understanding of this system more often than not leads to confusion, misdiagnoses, and the unnecessary replacement of parts and components. In addition, be aware that because of the differences in design specifics, this guide cannot provide detailed diagnostic and repair information for P2021 that will be valid for all applications under all conditions. For this reason, the generic information provided here should NOT be used in any diagnostic procedure for code P2021 without making reference to the manual for the application being worked on.

Nonetheless, the generic information provided here should enable most non-professional mechanics to diagnose and resolve code P2021 on most applications without too much effort or trouble. END OF SPECIAL NOTES.

OBD II fault code P2021 is a generic code that is defined by all manufacturers as “Intake manifold air control actuator position sensor/switch, bank 2- circuit low”, and is set when the PCM (Powertrain Control Module) detects an abnormally low voltage in the control circuit of the position sensor of the manifold airflow-control device. On engines with two cylinder heads, “Bank 2” refers to the bank of cylinders that does not contain cylinder #1.

The manifold airflow control device can be thought of as a second throttle plate, the purpose of which is twofold. On the one hand, it serves to regulate the speed at which the intake air flows through the manifold or in some designs, the speed at which the air/fuel mixture enters the cylinders, depending on the application. By increasing the speed of the airflow, atomization of the fuel is improved, which increases engine power without using more fuel because combustion is improved. This also reduces harmful exhaust emissions.

On the other hand, the manifold airflow control device largely regulates how fast the manifold fills up with air. For instance, under hard acceleration, the engine sucks the air/fuel mixture out of the manifold very quickly, and depending on the design of the engine (and the inlet manifold), engine performance can actually suffer if the air/fuel mixture cannot enter the manifold at the same rate that the engine uses it. Thus, by striking a balance between improving air flow (and therefore combustion), and increasing the speed at which the air/fuel mixture enters the manifold by slightly closing the flow control flaps, the volume of air in the inlet manifold can be maintained to within a very narrow margin to either side of the maximum volume that can be used by the engine under wide-open throttle conditions.

However, the devil lives in the details, and in this case, the devil demands that the degree of opening of the actual flaps that control the speed of the air flowing through the manifold should always match the engine speed and throttle setting. The relationship between the degree of opening, engine speed, and throttle setting at any given moment varies greatly between applications, but in a fully functional system, the position of the control flap(s) is monitored by either a position switch, or a position-sensing sensor that relays the actual position of the control flaps to the PCM.

Thus, if, on any given application, the actual position of the airflow control flaps does not match either the desired position of the control flaps, and/or the actual throttle setting and engine speed, engine performance can suffer because air cannot enter the manifold (or the cylinders) at the same rate that the engine uses it.

In terms of operation, the airflow control flaps are built into the inlet manifold, and their movement is controlled by a high-torque stepper motor (or vacuum solenoids on some designs) that is controlled by the PCM. Control inputs derive from both the position switch/sensor, and various other driveability sensors such as the MAP (Manifold Absolute Pressure) sensor – where fitted – , the MAF (Mass Airflow) sensor, TPS (Throttle Position) sensor, and others. Based on all of these inputs, as well as the feedback signal from the manifold airflow-control position sensor, the PCM calculates a desired position for the control flaps, and if everything works as intended, the control flaps will be either closed or opened by the stepper motor to a position that matches the desired position.

Regardless of the feedback signals received by the PCM from other sensors, the PCM will set code P2021 and illuminate a warning light when the feedback signal from the position sensor/switch that indicates the position of the manifold airflow control flaps is lower than expected. At this point, it should be noted that code P2021 is almost invariably caused by malfunctions of, or defects in, the position switch/sensor itself or in the wiring that is associated with the switch/sensor, and it is rare for this code to be caused by a failure of the mechanism(s) inside the inlet manifold.

The image below shows the typical layout of the main components of an intake manifold air control system. Note however that the design, appearance, and layout of these systems vary greatly between applications, but in this example, the position sensor/switch is circled in red, the actuator/stepper motor is circled in blue, the connection between the actuator and the common shaft is circled in green, and the dashed red line represents the axis of the common shaft that connects all the air control flaps in this manifold.

NOTE: Always refer to the manual for the application being worked on to locate, and identify all relevant components correctly, since on some applications, the various components of the manifold air control system may not look anything like the components in this example.

What are the common causes of code P2021?

Common causes of P2021 could include the following-

• Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
• Split, hardened, cracked, or dislodged vacuum lines
• Defective position switch/sensor
• Defective vacuum actuator or other vacuum operated component(s)
• Carbon deposits on the control flaps that prevent free movement of the flaps. Note however that this condition is likely to be indicated by a “Range/Performance related code along with P2021
• Failed or failing PCM. Note that this is a rare event, and the fault must be sought elsewhere before any controller is replaced.

What are the symptoms of code P2021?

Common symptoms of P2021 could include the following-

• Stored trouble code(s) and an illuminated, or sometimes flashing warning light
• Rough or fluctuating idle
• Hesitation or surging at some engine speeds, depending on the application
• Different applications will experience different degrees of power loss at some engine speeds and throttle settings

How do you troubleshoot code P2021?

NOTE: On systems that use engine vacuum to control/regulate the manifold airflow control system, a hand-held vacuum gauge fitted with a graduated gauge will be most helpful in diagnosing P2021.

Step 1

Record all fault codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on.

NOTE: If there are other codes present along with P2021, take careful note of them for future reference, since in some cases, especially on some Nissan applications, P2021 cannot be resolved before some accompanying codes are resolved first. Refer to the manual for the definitions of other codes, and take note of the possible implications of all other codes on P2021.

Step 2

Refer to the manual to locate and identify all components, associated wiring, and if applicable, all associated vacuum lines and related components. Also, determine the location, function, routing, and color-coding of all associated wiring to avoid mistakes and possible accidental short circuits.

Step 3

Once the position sensor/switch is located and identified, disconnect its wiring, and refer to the manual to determine the correct procedure (KOER/KOEO) to test the resistance of the sensor with a digital multimeter. Compare the obtained reading with the value stated in the manual, and replace the sensor if its resistance does not fall within the range specified by the manufacturer. Clear all codes after the replacement, and rescan the system to see if the code returns.

Step 3

If the code returns, reconnect the wiring, and prepare to test the operation of the sensor. This switch/sensor is usually a simple potentiometer that consists of a live pin that slides over a coiled resistor, which means that in the rest position, it will pass a specified current. As the slider moves over the coiled resistor, the voltage passed will either increase or decrease, depending on the application.

NOTE: On many, if not most, GM applications, many sensor values are often electrically opposite; meaning that while the signal voltage from this sensor will increase as the control flaps are opened on most applications, the signal voltage on this sensor on GM applications will decrease as the flaps are opened. Consult the manual on this very important point before proceeding to the next step.

Step 4

If the scanner can monitor live data streams, use it to monitor the sensor signal voltage as the control flaps are opened manually. Note that doing this manually will require that the actuator be disconnected from the common shaft, but be sure to follow the directions in the manual exactly on how to do this to prevent damaging anything.

The scanner will display a steady voltage (which should agree with the at-rest value in the manual), when the control flaps are in the at-rest position, and the increase in the signal voltage (or decrease, depending on the application), should happen smoothly as the flaps are opened to the fully open position. At this position, the displayed signal voltage should closely match the value specified in the manual.

NOTE #1: If any obtained readings deviate significantly from the specified values, consult the manual to identify the reference voltage wire, and check that the proper reference voltage (usually 5 volts) reaches the sensor. If the reference voltage checks out, replace the position sensor/switch.

NOTE #2: If a suitable scanner is not available, refer to the manual to identify the signal wire, and placing the probes of the multimeter into the connector from the back (aka “back probing”) slowly move the control flaps manually while observing the displayed reading. Both the fully closed, and fully open values displayed on the multimeter must match the values stated in the manual.

Step 5

If both the reference voltage and the sensor/switch’s internal resistance check out, but the code persists, disconnect the sensor/switch from the PCM and perform continuity, resistance, and ground connectivity checks on all relevant wiring as per the instructions in the manual.

Compare all obtained readings with the values stated in the manual. If any discrepancies are found, make repairs as required to ensure that all electrical values fall within the manufacturer’s specifications. Clear all codes after repairs are complete, and rescan the system to see if the code returns.

Note that if the sensor/switch has been replaced with an OEM part, and all electrical values fall within specified values, it is highly unlikely that the code will return at this point. However, if the code does return, it is likely that an intermittent fault is causing the problem, but be aware that intermittent faults can be extremely challenging and time consuming to find and repair. In some cases, it may be necessary to allow the fault to worsen considerably before an accurate diagnosis and definitive repair can be made.

Step 6

In nine instances out of every ten, the diagnostic/repair steps up to Step 5 will resolve P2021. However, on applications where the manifold airflow control system is regulated or controlled by engine vacuum, things are a little more complicated. On these applications, most of the components are made from plastic and rubber, neither of which is designed to withstand heat, vibration, and high under-hood temperatures for years on end without failing.

Thus, diagnosing P2021 on these applications will usually start with a thorough inspection of all associated vacuum lines. Look for hardened, cracked, split, or dislodged vacuum lines, and replace any vacuum line(s) that is/are not in a perfect condition.

Step 7

If all vacuum lines check out and no damage is found, locate the vacuum actuator, and attach the vacuum pump in place of the engine vacuum system. Consult the manual on the value of the maximum allowable vacuum, and draw this vacuum while monitoring the operation of the position sensor/switch either with the scanner, or with a multimeter. Refer to Steps 3, 4, and 5 above to interpret the result of this test.

NOTE: On many applications, the vacuum actuator is fitted with a filter to prevent dirt being drawn into the system. Be sure to check that this filter is not dirty, clogged, or otherwise unserviceable. Replace the filter element rather than attempt to wash or clean it.

Step 8

If the vacuum does not hold on the vacuum actuator and the test-equipment is not defective in any way, replace the actuator with an OEM part to prevent a recurrence of the code. Also, use this time to test all other vacuum operated components of the manifold airflow control system, and replace any that do not perform as intended.

NOTE: Some vacuum operated systems incorporate several one-way vacuum check valves. Be sure to identify them all, and make sure they all work as intended. These valves are intended to allow air to flow only in one direction; therefore, if the vacuum drawn on these check valve decay even in the slightest degree, replace that check valve.

Step 9

Clear all codes after all repairs are complete, but double check that all relearning procedures have been carried out where these are required. Operate the vehicle for at least one complete drive cycle with a scanner connected to monitor the operation of the manifold airflow control system in general, and the performance of the position switch/sensor in particular.

If the code does not return, the repair can be considered as successful. In the unlikely event that the code does return, repeat Steps 3, 4, and 5 to ensure that you have not missed anything. If needs be, perform a “wiggle” test on the position switch/sensor connector while monitoring its output to see if the voltage fluctuates. If it does fluctuate, repair or replace the connector.

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