If your 1993-1997 1.8L Toyota Corolla's MAP sensor is bad, you're gonna see one of these codes pop up in the system's memory:
- 1993-1995 OBD I Corolla: Code 31.
- 1996-1997 OBD II Corolla: Codes P0106, P0107, or P0108.
The good news is that you don't need an expensive scan tool to check if your MAP sensor's still good or fried. A simple multimeter is all it takes to run the test.
With your test results, you'll know for sure whether the sensor's working like it should or if it's time to replace it.
Contents of this tutorial:
- Symptoms Of A Bad MAP Sensor.
- Where To Buy The MAP Sensor And Save.
- TEST 1: Verifying The MAP Sensor Signal With A Multimeter.
- TEST 2: Making Sure The MAP Sensor Is Getting 5 Volts.
- TEST 3: Making Sure The MAP Sensor Is Getting Ground.
- The MAP Sensor Code Won't Go Away.
- More 1.8L Toyota Corolla Tutorials.
NOTE: This tutorial applies to the following vehicles:
- 1.8L (7A-FE) Toyota Corolla: 1993, 1994, 1995, 1996, 1997.
- 1.8L Geo Prizm: 1993, 1994, 1995, 1996, 1997.
Symptoms Of A Bad MAP Sensor
The 1993-1997 1.8L Toyota Corolla uses a speed density fuel injection system. In layman's terms, this means the computer figures out how much air the engine's pulling in by using three main inputs:
- Engine RPM: This input comes from the distributor pickup coil (1993-1994) or the crankshaft position (CKP) sensor (1995-1997).
- Intake air temperature: Provided by the intake air temperature (IAT) sensor.
- Intake manifold pressure: Provided by the manifold absolute pressure (MAP) sensor.
Since the MAP sensor plays such a big role in this setup, when it fails, the engine is definitely gonna resent it and engine performance is gonna suffer.
Here's what you might notice:
- Check engine light (CEL): The CEL will be illuminated and the computer will store a MAP sensor related diagnostic trouble code (DTC).
- OBD I Diagnostic trouble code (1993-1995): The stored code will be:
- Code 31: MAP Sensor Circuit.
- OBD II Diagnostic trouble codes (1996-1997): You'll see one of these codes:
- P0106: MAP Sensor Circuit Range/Performance Problem.
- P0107: MAP Sensor Circuit Low Input.
- P0108: MAP Sensor Circuit High Input.
- Engine struggling to start: The engine might not start at all, or you'll have to crank it for a while before it finally fires up.
- Black smoke and bad fuel economy: You'll see black smoke from the exhaust as the engine runs and especially when you step on the gas pedal.
- Bad gas mileage: You'll see a big drop in gas mileage.
- Rough idle and weak acceleration: The engine won't idle smoothly, and pressing the gas won't give you the power you're used to.
MAP Sensor Circuit Descriptions
| Corolla MAP Sensor Pinout | ||
|---|---|---|
| Pin | Wire Color | Description |
| 1 | Brown (BRN) | Sensor Ground |
| 2 | Light Green with red stripe (LT GRN/RED) | MAP Signal |
| 3 | Yellow (YEL) | 5 Volts |
To successfully diagnose the manifold absolute pressure (MAP) sensor as good or bad, it helps to know a little about how it functions.
This sensor outputs a voltage signal that changes depending on the vacuum (or pressure) inside the intake manifold. This signal (known as the MAP signal) helps the fuel injection computer keep track of engine load and tweak fuel delivery as needed.
- At idle or light load: The intake manifold vacuum is high, so the MAP sensor sends out a low voltage signal, usually between 0.5 to 1.5 Volts DC.
- Under heavy load: When you hit the gas, the vacuum drops, and the sensor's voltage climbs. At wide-open throttle (low vacuum), it can hit 4.5 to 5 Volts DC.
If the MAP sensor fails, one of the most common problems is that its voltage signal gets stuck at a fixed value, no matter what the engine is doing.
When that happens, the computer is flying blind and switches to "limp-in" mode. Fuel delivery is no longer fine-tuned to actual engine operating conditions, which hurts performance. Emissions will also increase, and a MAP sensor DTC will trigger the check engine light.
Where To Buy The MAP Sensor And Save
You can find the MAP sensor in just about any auto parts store, but I think you'll find the better price online. The following MAP sensors are pretty good deals:
Not sure if the MAP sensors in the links above fit your Toyota Corolla? Don't worry, once you get to the site they will ask you the specifics of your vehicle and make sure it fits. If it doesn't fit they will find you the right one.
TEST 1: Verifying The MAP Sensor Signal With A Multimeter
This first test gets things rolling by checking whether the MAP sensor's actually putting out a signal. Depending on what you find, you'll either conclude that the MAP sensor is functioning correctly or move on to TEST 2.
The instructions below assume that you're using a vacuum pump. If you're in the USA and don't have one, places like AutoZone or O'Reilly Auto Parts let you rent one for free (you leave a small deposit, which is refunded when you return the tool).
No vacuum pump? No problem. You can DIY it by attaching a vacuum hose to the MAP sensor's inlet and using your mouth to create suction —the classic lung-powered method!
IMPORTANT: For this test to work, the MAP sensor must stay plugged into its electrical connector. To tap into the signal, use a back probe or a wire-piercing probe to check the signal wire. You can see an example of this tool here (and where to buy it): Wire Piercing Probe.
Alright, here's what you gotta do:
- 1
Pull the MAP sensor's vacuum hose off.
- 2
Hook up your vacuum pump to the MAP sensor's vacuum inlet.
- 3
Set your multimeter to Volts DC.
- 4
Attach the red multimeter lead to the wire connected labeled with the number 2 (see photo above) using the right probing tool.
IMPORTANT: The MAP sensor has to stay plugged into its 3-wire connector. - 5
Connect the black multimeter lead to the battery's negative (-) terminal.
- 6
Turn the key to the ON position but don't crank or start the engine.
This powers up the MAP sensor and gives it a Ground connection. - 7
Your multimeter should read about 4.7 Volts DC at this point.
- 8
Apply vacuum to the MAP sensor using either the vacuum pump (or just your mouth).
- 9
The voltage reading on the multimeter should drop.
- 10
Let go of the vacuum you applied to the MAP sensor.
- 11
The voltage should climb back up to whatever value you saw in step 7.
Alright, let's break down what your test results mean:
CASE 1: The voltage smoothly increased and decreased without any gaps. This is the correct and expected result.
This tells you that the MAP sensor's working just fine, and it's not the cause of the MAP sensor code or issue on your 1.8L Toyota Corolla.
If the MAP sensor code is still triggering the check engine light on your dashboard, check out this section: The MAP Sensor Code Won't Go Away for more details.
CASE 2: The voltage stayed stuck at one value. This points to a faulty MAP sensor.
To confirm the sensor's bad, make sure it's getting 5 Volts and Ground. Head over to: TEST 2: Making Sure The MAP Sensor Is Getting 5 Volts.
CASE 3: Your multimeter showed 0 Volts. This usually means the MAP sensor's fried.
But just to be sure, check that the MAP sensor is getting power and Ground. If both are present, the sensor's definitely bad. Go to: TEST 2: Making Sure The MAP Sensor Is Getting 5 Volts.