MAP Sensor (Manifold Absolute Pressure)
Location, connector pinout, test procedure, and related fault codes for the intake manifold pressure sensor on Class 8 diesel trucks.
Last updated: 2026-09-20
Overview
The MAP (Manifold Absolute Pressure) sensor measures boost pressure in the intake manifold. The ECM uses this reading to control fuel delivery, EGR flow, and VGT position. A failed MAP sensor causes the ECM to run in open-loop boost control, resulting in derate, black smoke, or low power.
Sensor Locations by Platform
Cummins X15
Intake manifold — driver side, near front of engine. Threaded into manifold boss.
X15 may have two MAP sensors — verify which one is faulting.
PACCAR MX-13
Intake manifold — driver side, rear of engine. Threaded into manifold.
MX-13 MAP sensor connector is known for moisture ingestion.
Detroit DD15
Intake manifold — driver side. Threaded into manifold near EGR inlet.
DD15 MAP sensor port can plug with EGR soot — clean port during replacement.
Volvo/Mack MP8
Intake manifold — passenger side, near front of engine.
D13/MP8 MAP sensor is integrated with IAT sensor on some applications.
DieselVision™ identifies sensor labels and connector pin numbers — upload a close-up photo and the system maps pins automatically.
Connector Pinout
| Pin | Function | Specification |
|---|---|---|
| A | 5V Reference | 4.75–5.25V (key on, engine off) |
| B | Ground (Signal Return) | <0.1V to chassis ground |
| C | Signal Output | 0.5V at 0 PSI boost, ~2.0V at atmospheric (14.7 PSI), 4.5V at max boost |
Test Procedure
Key on, engine off — read MAP sensor voltage in live data
Expected: ~1.5–2.0V (atmospheric pressure, 14.7 PSI). Varies with altitude.
Tool: OEM diagnostic software
Measure 5V reference voltage at harness connector (sensor disconnected)
Expected: 4.75–5.25V between pin A and pin B
Tool: Multimeter
Measure ground circuit resistance from pin B to chassis ground
Expected: <0.5 ohms
Tool: Multimeter
Check signal wire for short to ground (sensor disconnected, key off)
Expected: >1 MΩ between pin C and chassis ground. Low resistance = short to ground
Tool: Multimeter
Start engine and monitor MAP sensor voltage at idle and under load
Expected: Voltage increases with boost. At idle: ~1.5–2.0V. Under load: up to 4.0V
Tool: OEM diagnostic software
Inspect MAP sensor port for oil or carbon plugging
Expected: Port should be clear. Plugged port causes false low reading
Tool: Visual inspection
Common Failure Modes
- •Internal sensor failure — signal stuck high or low
- •Connector corrosion causing intermittent signal
- •Sensor port plugged with oil mist or EGR soot
- •Signal wire short to ground (FMI 4)
- •Signal wire short to voltage (FMI 3)
- •Open circuit in signal wire (FMI 4)
Frequently Asked Questions
Where is the MAP sensor located on a Cummins X15?
On the Cummins X15, the MAP sensor is threaded into the intake manifold on the driver side, near the front of the engine.
What voltage should a MAP sensor read at key on, engine off?
At key on, engine off, a MAP sensor should read approximately 1.5–2.0V, representing atmospheric pressure (14.7 PSI). This varies slightly with altitude.
What causes a MAP sensor to read low?
Common causes include a plugged sensor port (oil mist or EGR soot), signal wire short to ground, or internal sensor failure.
What fault codes are caused by a failed MAP sensor?
Common fault codes include SPN 102 FMI 3 (voltage above normal), SPN 102 FMI 4 (voltage below normal), and SPN 1127 FMI 16 (boost pressure above normal).
Snap a photo of your scan tool screen and let Diesel Vision interpret the fault instantly — no manual code lookup required.
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