The manifold air temperature (MAT) sensor is an important component in the speed-density fuel injection system of your 2.5L Chevy S10 pickup (GMC S15 pickup, GMC Sonoma).
In this tutorial, I'll be explaining everything you need to know about the MAT sensor, including its role, symptoms of a faulty sensor, common problems, and how to test it.
The MAT sensor test I'll be sharing is explained step by step and doesn't require any expensive diagnostic tools. Let's get testing!
NOTE: The manifold air temperature (MAT) sensor is also known as the intake air temperature (IAT) sensor.
Contents of this tutorial:
- Symptoms Of A Bad Manifold Air Temperature (MAT) Sensor.
- Role OF Manifold Air Temperature (MAT) Sensor.
- Common Manifold Air Temperature (MAT) Sensor Problems.
- What Tools Do I Need To Test The MAT Sensor?.
- TEST 1: Checking For MAT Sensor Trouble Codes.
- TEST 2: Checking For An Internal Open-Circuit/Short-Circuit Issue.
- TEST 3: Checking Temperature To Resistance Value Relationship.
- More 2.5L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials.
APPLIES TO: This tutorial applies to the following vehicles:
- 2.5L Chevrolet S10 Pickup: 1988, 1989, 1990, 1991, 1992, 1993.
- 2.5L GMC S15 Pickup: 1988, 1989, 1990.
- 2.5L GMC Sonoma: 1991, 1992, 1993.
Symptoms Of A Bad Manifold Air Temperature (MAT) Sensor
There are several symptoms that may indicate a faulty MAT sensor. These symptoms can include:
- Engine performance problems.
- Poor fuel economy.
- Engine misfires.
- Engine stalling.
- Engine hesitation.
- Increased emissions.
- Extended cranking time (got to crank the engine a while before it starts).
- Engine does not start.
A faulty MAT sensor will set one of the following diagnostic trouble codes:
- Code 23: MAT (Manifold Air Temperature) Signal Voltage High.
- Code 25: MAT (Manifold Air Temperature) Signal Voltage Low.
Role OF Manifold Air Temperature (MAT) Sensor
The manifold air temperature (MAT) sensor's single purpose in life is to measure the temperature of the air entering the engine and provide this info the the engine control module (ECM).
The ECM uses this information to calculate the density of the air and adjust the air/fuel mixture accordingly, which affects engine performance, fuel economy, and emissions.
The MAT sensor is a crucial component in the engine management system, and as noted in the previous section, if it fails, it can lead to engine performance problems, lower fuel efficiency, and increased emissions.
Common Manifold Air Temperature (MAT) Sensor Problems
There are several common problems that can cause a MAT sensor to fail.
- A break in the circuit inside the MAT sensor has occurred causing an internal open-circuit problem.
- A direct connection between two points in the circuit inside the MAT sensor has occurred causing an internal short-circuit problem.
- The insulation on the wires of the MAT sensor connector has peeled off and the wires are shorted together.
- The locking tab on the MAT sensor connector is broken, resulting in an intermittent connection between the sensor and the ECM.
Any of these conditions will cause the sensor to send an incorrect signal to the engine control module (ECM), resulting in engine performance problems, as well as setting diagnostic trouble codes (DTCs).
What Tools Do I Need To Test The MAT Sensor?
To test the MAT sensor, you'll need a few tools.
- A multimeter.
- A code reader.
A scan tool, which can be quite expensive if it has the capability to work with OBD I systems, is not necessary to test the manifold air temperature (MAT) sensor.
While a code reader is a helpful tool, it's not required to complete the tests outlined in this tutorial.
What is a must-have tool for the MAT sensor test is a multimeter. I have a few recommendations if you're looking for a fully-featured yet budget-friendly option: Buying A Digital Multimeter For Automotive Diagnostic Testing.
Initial Checks Before Starting The MAT Sensor Tests
Before performing the MAT sensor test, there are a few initial checks that should be made.
- Inspect the MAT sensor connector wires for any damage, such as cuts or fraying.
- Inspect the MAT sensor connector for any damage, such as cracks or a broken locking tab.
- Inspect the MAT sensor for any damage, such as cracks or corrosion.
A frayed wire is a wire that has become damaged and its metallic innards have become exposed. This is a common problem that occurs with the manifold air temperature (MAT) sensor connector. Here's an example:
Frayed wires can cause issues such as a short-circuit, which can result in incorrect readings from the MAT sensor.
To determine the severity of the fraying, inspect the wire carefully. If the fraying is severe or near the connector, it's best to replace the entire connector.
If the fraying is not severe and far enough from the connector, wrapping the frayed section with layers of electrical tape can provide a temporary fix.
However, it is important to note that electrical tape is only a temporary solution and that replacing the connector is the only way to ensure a permanent fix.
The MAT sensor connector is easily available at local auto parts stores or online.
TEST 1: Checking For MAT Sensor Trouble Codes
The first step in troubleshooting your vehicle's engine performance issue is to check for diagnostic trouble codes related to the manifold air temperature (MAT) sensor.
This can be done either with a code reader or by manually reading the ON/OFF flashes of the check engine light.
If you don't have a code reader, don't worry! The first generation onboard diagnostic (OBD) system on your 2.5L Chevy S10 pickup (GMC S15 pickup, GMC Sonoma) allows you to manually retrieve the diagnostic trouble codes.
I've put together a step-by-step tutorial on how to retrieve the codes manually, and it's available right here: How To Retrieve OBD I Trouble Codes (1986-1993 2.5L Chevy S10 Pickup, GMC S15 Pickup, GMC Sonoma) .
Let's dive right in:
- 1
Locate the onboard diagnostic (OBD) port in your vehicle
This is usually located under the dashboard near the steering wheel. - 2
Connect the code reader to the OBD I port.
- 3
Turn the ignition key to the ON position but don't start the engine.
- 4
Follow the code reader's instructions to retrieve the diagnostic trouble codes.
- 5
Write down the codes.
Is code 23 MAT (Manifold Air Temperature) Signal Voltage High present?
Is code 25 MAT (Manifold Air Temperature) Signal Voltage Low present
Let's see what your test results mean:
CASE 1: MAT sensor codes are present. Now that you've confirmed that the ECM is aware of a MAT sensor problem, your next step is go to: TEST 2: Checking For An Internal Open-Circuit/Short-Circuit Issue.
CASE 2: MAT sensor codes ARE NOT present. It looks like we've ruled out the manifold air temperature (MAT) sensor as the cause of your engine performance issue.
Since no codes related to the MAT sensor were found, you can conclude that at this moment the MAT sensor is functioning properly.
