Quite a few things can fool your Honda's PCM (Powertrain Control Module = fuel injection computer) into thinking the manifold absolute pressure (MAP) sensor is bad when it isn't.
Thankfully, testing the MAP sensor is pretty easy and in this tutorial I'll show you how to bench-test it using only a multimeter.
Here are the contents of this tutorial at a glance:
- Symptoms Of A Bad MAP Sensor.
- How The MAP Sensor Works.
- Circuit Descriptions Of The MAP Sensor.
- START HERE: How To Diagnose The MAP Sensor.
- TEST 1: Verifying The MAP Sensor Has Power.
- TEST 2: Verifying The MAP Sensor Has Ground.
- TEST 3: Verifying The MAP Signal With A Multimeter.
- MAP Sensor Is Good But Code Doesn't Go Away!
- Where To Buy Your Honda Civic's MAP Sensor Cheaper.
- More Honda Test Tutorials.
You can find this tutorial in Spanish here: Cómo Probar El Sensor MAP (1995-2000 1.6L Honda Civic) (at: autotecnico-online.com).
Symptoms Of A Bad MAP Sensor
Since the MAP sensor's vacuum pressure input is used to calculate engine load and thus fuel injection and timing advance when it fails, the PCM won't be able to keep your 1.6L Honda Civic running smoothly. You'll see one or more of the following symptoms:
- Check engine light (CEL) is shining nice and bright on the instrument cluster.
- DTC P0107 MAP Sensor Circuit Low Voltage.
- DTC P0108 MAP Sensor Circuit High Voltage.
- Rough idle.
- ‘Rotten egg’ smell coming from the exhaust.
- Won't pass the state mandated emissions test.
- Bad gas mileage.
- Lack of power, rough idle, or hesitation.
- Engine cranks a long time before starting.
Let's find out how the MAP sensor works on your Civic in the next subheading.
How The MAP Sensor Works
Your Honda Civic's fuel system is a speed density type. Which, in plain English means that your Honda's fuel injection computer needs to know the engine speed and the engine load to inject the proper amount of fuel (advance ignition timing, etc.).
The sensor that provides engine load information, to the PCM, is the manifold absolute pressure (MAP) sensor.
How does the MAP provide this engine load info? By measuring the amount of vacuum the engine is creating throughout the entire time it's operating.
The amount of vacuum pressure varies depending on engine load. Here are some more specifics:
- At idle, manifold vacuum is higher.
- When manifold vacuum is higher, the MAP sensor sends the PCM a higher voltage.
- The PCM, using the inputs from the MAP sensor and other sensors, injects less fuel into all its cylinders.
- Under load (let's say accelerating the engine to pass someone on the highway), manifold vacuum is lower.
- When manifold vacuum is lower, the MAP sensor sends the PCM a smaller voltage.
- The PCM, using the inputs from the MAP sensor and other sensors, injects more fuel into all its cylinders.
Circuit Descriptions Of The MAP Sensor
If you have already identified the manifold absolute sensor on your Honda Civic, you know that its connector has 3 wires coming out of it.
Each one of those wires (circuits) has a specific job to do.
These circuits are the ones that provide power, ground and return the MAP signal (that the manifold absolute pressure (MAP) sensor creates) to the PCM.
Here's a brief description of the function of each:
- One wire supplies 5 Volts DC.
- This is the MAP sensor's power source.
- 5 Volts are fed only with the Key On Engine OFF (KOEO) or Key On Engine Running (KOER).
- The fuel injection computer (PCM) feeds these 5 Volts to the MAP sensor.
- MAP sensor pin labeled with the number 1, in the image above, gets this power.
- One wire feeds ground.
- In tech circles, this circuit is know as the low reference circuit.
- The PCM provides this ground internally.
- Ground provided by the middle wire of the MAP sensor connector. MAP sensor pin labeled with the number 2, in the image above, gets this ground.
- One wire is the MAP sensor signal circuit.
- This wire sends the signal the MAP sensor creates to the computer (PCM).
- MAP sensor pin labeled with the number 3, in the image above, outputs the MAP signal to the PCM.