P2021Generic code

P2021 Code: Intake Manifold Runner Position Sensor/Switch Circuit Low (Bank 2)

The P2021 code means the signal from the intake manifold runner position sensor on bank 2 is below its minimum value. The main effect is that the computer cannot verify where the flaps are and may leave them in a fixed position. The engine runs, with a little less performance.

Severity
Low
Can I keep driving?
Yes, no immediate risk
Estimated cost
$40 to $350
Difficulty
Medium
System
Air and Fuel
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P2021 code means

Many engines have flaps or valves in the intake manifold (IMRC, Intake Manifold Runner Control, also called swirl or tumble flaps) that change the length or shape of the intake runner. At low rpm they close so the air enters faster and with more turbulence, which improves torque and combustion. At high rpm they open to let more air through. An electric motor or a vacuum actuator controlled by a solenoid moves them, and a position sensor tells the computer whether they really moved.

The sensor gets a 5 volt reference and a ground from the computer and sends back a signal somewhere between about 0.5 and 4.5 volts. The P2021 code is a low signal, which is usually caused by the signal wire shorted to ground or by a missing reference voltage.

The sensor is mounted on the end of the flap shaft or inside the actuator. Bank 1 is the side of the engine where cylinder number 1 is. Inline engines only have bank 1. On V engines, bank 2 is the opposite side.

To confirm the diagnosis, unplug the component with the key on and see what happens to the reading or the code. If the value jumps to the opposite extreme, the wiring is fine and the component is the part pulling the signal to ground. If nothing changes, go hunting for the short in the wire, starting where the harness rubs against the engine, the chassis or the exhaust.

P2021 code symptoms

  • Check engine light on.
  • The computer cannot verify the position of the flaps and may leave them in a fixed position.

Likely causes of the P2021 code

  1. Signal wire shorted to ground where the harness rubs against the engine, the chassis or a bracket.
  2. Reference supply shorted. If several sensors fail at once, suspect the shared reference.
  3. Damaged sensor with an internal short.
  4. Connector with water or corrosion, which creates a path to ground.

How to diagnose the P2021 code step by step

  1. Read the sensor value on the scan tool and compare it with what you expect.
  2. Inspect the connector for corrosion, water or loose pins.
  3. Check power and ground with the key on: the reference should be correct and the voltage drop on the ground should be under 0.1 volt.
  4. Measure the signal with the connector plugged in and see whether it changes with the condition.
  5. Do a wiggle test on the harness with the scan tool in graph mode.
  6. Check the continuity of each wire to the computer. It should be under 1 ohm.

How to fix the P2021 code

  • Repair the connector or the wiring.
  • Replace the sensor if the tests confirm it is bad.
  • Correct the real condition if there is one.
  • Clear the codes and verify the repair with a road test.

Technical reference data

  • Vacuum actuator: it should hold about 15 to 20 inHg without losing vacuum for one minute.
  • Electric actuator: 12 volt supply, with control by a PWM signal or by reversing polarity.
  • Position sensor: 5 volt reference and a signal of roughly 0.5 to 4.5 volts depending on the flap position.
  • These values are only a guide, so look up the manufacturer data for your vehicle.

Brand-specific notes

On some diesels the flaps fill up with carbon and can break. A fragment inside the cylinder can cause a serious failure, so some shops remove the flaps following manufacturer procedures.

P2021 on Ford and Mazda

This code is frequent on Ford Duratec and Mazda MZR gasoline engines.

P2021 on Volkswagen, BMW, Mercedes-Benz and Fiat

It is also frequent on the diesel engines with swirl flaps from Volkswagen, BMW, Mercedes-Benz and Fiat.

P2021 on GM V6 Engines

Several GM V6 engines are also known for this code.

Frequently asked questions about P2021

Can I drive with a P2021 code?
Yes. The engine runs, with a little less performance.
Does the sensor have to be replaced?
Only if the tests confirm it. The connector and the wiring fail just as often as the sensor.
What does the intake manifold runner position sensor on bank 2 do?
Many engines have flaps in the intake manifold (IMRC, also called swirl or tumble flaps) that change the length or shape of the runner. They close at low rpm to speed up the air and open at high rpm to let more through. The position sensor tells the computer whether the flaps really moved.
How much does it cost to fix P2021?
Roughly $40 to $350, depending on whether it is a connector, a wire or the sensor.
What does the P2021 code mean?
It is a generic OBD2 code that means the signal from the bank 2 intake manifold runner position sensor is below its minimum value. A signal wire shorted to ground is the classic cause.
Will a P2021 code clear itself?
Only if the cause was a passing glitch. A chafed wire or a wet connector will bring the P2021 code back.
What is the most common cause of P2021?
The signal wire rubbing through against the engine, the chassis or a bracket and touching ground. A wet or corroded connector can do the same thing.

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