Faulty intake air low pressure switch (stuck closed or internally shorted); Short to ground in the signal circuit between the switch and the PCM; Damaged or disconnected vacuum hose to the pressure switch; Corroded or loose electrical connector at the switch; Failed PCM (rare, but possible if all other causes are ruled out); Intake air restriction or blockage causing abnormal pressure readings

DTC codes / GM codes / P1420

P1420 · GMIntake Air Low Pressure Switch Circuit Low Voltage

Q: What does code P1420 mean?

Intake Air Low Pressure Switch Circuit Low Voltage. P1420 on GM vehicles indicates that the intake air low pressure switch circuit is reporting a low voltage condition to the powertrain control module (PCM). The PCM monitors this switch to verify that the intake air system is functioning within expected pressure ranges, and a low voltage signal typically means the switch is closed when it should be open or the circuit is shorted to ground.

P1420 on GM vehicles indicates that the intake air low pressure switch circuit is reporting a low voltage condition to the powertrain control module (PCM). The PCM monitors this switch to verify that the intake air system is functioning within expected pressure ranges, and a low voltage signal typically means the switch is closed when it should be open or the circuit is shorted to ground.

SystemPowertrain

Code typeGM specific

SeverityMedium

Fix difficultyIntermediate

AreaAuxiliary emission controls

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Reduced engine performance or power, especially during acceleration
Rough idle or stumbling when the engine is cold
Poor fuel economy due to incorrect air pressure readings
In rare cases, the engine may enter limp mode or exhibit hesitation

Common causes, most likely first

Faulty intake air low pressure switch (stuck closed or internally shorted)
Short to ground in the signal circuit between the switch and the PCM
Damaged or disconnected vacuum hose to the pressure switch
Corroded or loose electrical connector at the switch
Failed PCM (rare, but possible if all other causes are ruled out)
Intake air restriction or blockage causing abnormal pressure readings

How to diagnose and fix it

Inspect the vacuum hose connected to the intake air low pressure switch for cracks, disconnection, or blockage, and replace if necessary
Check the electrical connector at the switch for corrosion, tightness, and proper pin fit; clean or repair as needed
Measure the voltage on the signal circuit at the switch with the key on and engine off; compare to specification (typically 5V reference or ground depending on design)
Test the switch operation using a vacuum pump and multimeter to verify it opens and closes at the correct pressure threshold
Disconnect the PCM and check for a short to ground on the signal circuit; repair wiring if resistance is below specification
If the switch and wiring are good, substitute a known-good switch and clear the code to see if it returns
As a last resort, diagnose the PCM for internal faults following GM service procedures

Don't overlook the simple vacuum line

A disconnected or cracked vacuum hose at the pressure switch is one of the most common causes of P1420 and is often missed during visual inspections.
The intake air low pressure switch is sometimes confused with the manifold absolute pressure (MAP) sensor, but they serve different functions and have distinct circuits.
A low voltage code can be set by a switch that is stuck closed due to debris or carbon buildup, not just by wiring problems.
On some GM engines, the switch is part of the intake air heater circuit, so a fault there can trigger P1420 without any driveability symptoms.
Clearing the code without repairing the underlying issue will usually result in the code returning after a few drive cycles.

Can I keep driving with P1420?

You can generally continue driving with P1420, but avoid heavy acceleration or towing until the fault is repaired, as incorrect air pressure readings may affect engine performance and fuel economy. If the engine runs poorly or enters limp mode, seek service promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.