Faulty intake manifold pressure (MAP) sensor.; Damaged or corroded wiring or connector at the MAP sensor.; Vacuum leak in the intake manifold or associated hoses, causing incorrect pressure readings.; Clogged or restricted vacuum port to the MAP sensor.; Failed PCM (rare, but possible after other causes are ruled out).; Electrical interference or poor ground connection affecting the sensor signal.

DTC codes / GM codes / P1408

P1408 · GMIntake Manifold Pressure Sensor Circuit

Q: What does code P1408 mean?

Intake Manifold Pressure Sensor Circuit. P1408 is a GM-specific code indicating that the powertrain control module (PCM) has detected an abnormal signal from the intake manifold pressure (MAP) sensor circuit. The PCM monitors the MAP sensor voltage and compares it to expected values for the current engine operating conditions; when the signal falls outside the acceptable range or is inconsistent with other sensor inputs, it sets this code.

P1408 is a GM-specific code indicating that the powertrain control module (PCM) has detected an abnormal signal from the intake manifold pressure (MAP) sensor circuit. The PCM monitors the MAP sensor voltage and compares it to expected values for the current engine operating conditions; when the signal falls outside the acceptable range or is inconsistent with other sensor inputs, it sets this code.

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.
Rough idle or stalling, especially when the engine is cold or under load.
Hesitation or stumble during acceleration.
Poor fuel economy due to incorrect air/fuel mixture calculations.
Black smoke from the exhaust or a strong fuel odor indicating a rich condition.
In some cases, the engine may run lean and cause surging or misfires.

Common causes, most likely first

Faulty intake manifold pressure (MAP) sensor.
Damaged or corroded wiring or connector at the MAP sensor.
Vacuum leak in the intake manifold or associated hoses, causing incorrect pressure readings.
Clogged or restricted vacuum port to the MAP sensor.
Failed PCM (rare, but possible after other causes are ruled out).
Electrical interference or poor ground connection affecting the sensor signal.

How to diagnose and fix it

Inspect the MAP sensor connector and wiring for damage, corrosion, or loose pins; repair as needed.
Check for vacuum leaks using a smoke machine or propane enrichment test, and repair any leaks.
Test the MAP sensor with a multimeter or scan tool to verify its voltage output matches manufacturer specifications; replace if faulty.
Verify the sensor's vacuum port is clear and free of carbon buildup; clean if necessary.
Check the sensor's reference voltage and ground circuits for continuity and correct voltage.
If all else checks out, substitute a known-good MAP sensor to see if the code resolves.
Clear the code and perform a drive cycle to confirm the repair.

Don't overlook vacuum leaks or wiring

A common misdiagnosis is replacing the MAP sensor when the real problem is a vacuum leak elsewhere in the intake system, such as a cracked intake manifold gasket or a disconnected vacuum hose.
Corroded or chafed wiring near the MAP sensor connector is frequent on older GM vehicles, especially where the harness rubs against the engine cover or intake tubing.
The code can be set by a MAP sensor that is 'lazy' and responds slowly to pressure changes, even if it reads correctly at idle; a scan tool graph of MAP voltage during a snap-throttle test can reveal this.
On some GM engines, a dirty throttle body or a failing throttle position sensor can cause inconsistent MAP readings that trigger P1408, so those should be checked if the MAP circuit tests good.
P1408 is sometimes stored alongside P0106 or P0107, which are generic MAP-related codes, so diagnosing the root cause requires looking at all related codes and freeze-frame data.

Can I keep driving with P1408?

You can usually drive the vehicle with P1408 set, but expect reduced performance and fuel economy, and avoid heavy acceleration or towing until the fault is repaired. If the engine runs very poorly or stalls frequently, it is safer to limit driving to a short distance to a repair shop.

Tools that help

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