Your car's ambient temperature sensor is responsible for reading the air temperature and sending that information to the engine control unit. This helps the ECU determine how much fuel to inject into the engine. Unfortunately, a bad ambient temperature sensor can cause all sorts of problems with your car, including decreased fuel efficiency, rough running, and even damage to the engine. In this article, we'll discuss the symptoms of a bad ambient temperature sensor, how to diagnose it, and how to repair it.
What is an ambient temperature sensor, and what does it do?
The ambient temperature sensor is a small device found on the intake manifold, radiator, or even near the headlights. It has one wire attached to it that goes into the car's engine control unit.
The ECU takes the information from this sensor and tells your car's computer how much fuel needs to be injected into your engine for optimal performance.
The ambient temperature sensor works by measuring the temperature of the outside air. This is a variable resistor or a device that changes its electrical resistance depending on how hot or cold it is.
As the name implies, this part detects ambient temperatures around your car. So, for example, when you're driving in wintertime, and your windows become fogged up from the cold air inside the car, this is due to the small amount of heat coming out of your heater.
This device reads that temperature and relays it to the ECU, which then tells your car how much fuel to inject into its cylinders for optimal performance.
10 Symptoms of a bad ambient temperature sensor
Here are ten potential problems that may arise if your ambient temperature sensor is malfunctioning:
- Engine Light turning on
- Rough running or misfiring
- Engine can stall
- Sluggish acceleration
- Decreased fuel economy
- The engine feels like it's just not getting enough air or fuel and hesitates when accelerating.
- Car runs hotter than usual
- Loss of power
- Slow to warm up in cold weather
- Engine overheats, even when the ambient temperature is cool
How to diagnose a bad ambient temperature sensor?
Diagnosing the ambient temperature sensor is not complicated and doesn't require intensive labor or advanced tools. However, there are some instances where you might need to consult a mechanic to inspect the ambient temperature sensor further.
Here are ten things you can do to determine whether your ambient temperature sensor is causing problems with your car.
Test your car's battery voltage.
If your battery voltage is less than 12.8 volts, it could be that the ambient temperature sensor doesn't have enough power to send a signal to the engine control unit. If this is the case, you'll have to have your car's battery tested and possibly replaced.
Test for a bad ground
If your car has bad ground and it's causing your engine to stall out, you're going to want to fix the problem. For example, corroded metal connectors can cause bad ground on your engine, loose wiring under the hood, or corrosion on some brake lines.
Have your mechanic look at the wiring harness
Have your mechanic inspect the wiring if you think that the problem may be with your car's wiring harness. If the insulation on your wires is damaged or deteriorated, it can result in poor conductivity or even short out sections of wiring harnesses.
Install a new intake manifold gasket
The engine control unit communicates through the intake manifold gasket with the ambient temperature sensor. So if the intake manifold gasket is leaking, there's a chance that it can be interfering with communication between those two components.
Inspect the wiring harness
If you reinstall a new intake manifold gasket and the problem continues, it may be caused by damaged wiring. Check your wiring harness for any signs of wear or damage.
Test for a bad temperature sensor
You can test the ambient temperature sensor by turning your car on and letting it idle. Then, use a digital multimeter to see if the sensor shows any voltage. If it's not, then you either have a broken wire in your wiring harness or a malfunctioning ECU.
Check for loose connections.
If all of these tests come back negative and your ambient temperature sensor is still giving you trouble, there's a chance that it's just loose. Make sure all of the electrical connections in your car are tight and secure, including the connectors to the ECU.
Replacing your ambient temperature sensor
The ambient temperature sensor is not an expensive part, so you might not ever need to replace it depending on what's wrong with it. However, if you do need to replace it, there are two types that you can get. One is called a barometric pressure sensor, and the other is an air charge temperature sensor.
You could also go with one of our universal sensors. We have universal cold air temperature sensors, universal intake air temperature, and universal ambient temperature sensors .
If you need help finding the right part for your car, use our Locator Service. Just enter your vehicle details, and it will find all of the parts that are guaranteed to fit.
How to repair a bad ambient temperature sensor?
In many instances, a bad temperature sensor is associated with a trouble code P0128, which means the ambient temperature sensor isn't working properly. The engine control unit calculates the readings from this sensor to determine your car's ideal operating conditions so that it can adjust accordingly.
If your car starts having these sorts of problems where the engine runs hot even though the ambient temperature is low, you might want to check and make sure that this sensor isn't broken or malfunctioning. If it's not working correctly, your car will have trouble maintaining a consistent coolant temperature, hurting your fuel economy and engine performance.
To replace this sensor, you're going to have to remove your car's intake manifold and then unplug the wires that attach to this sensor. You'll then bolt on a brand new ambient temperature sensor and plug in all necessary wiring.
Your mechanic will be able to test the input from your cold air intake temperature sensor, so you don't have to go digging around under your hood when you suspect that this is the problem. If it's broken, he can easily replace it for you in about an hour without having to do any major work.
If your car still has problems after replacing your ambient temperature sensor, the chances are good that there's a wiring issue or something else wrong with your intake manifold gasket. So first, ensure all connections are secure and properly sealed, and then test drive your car again to see if you get any error codes.
If it's not a wiring or gasket issue and you're still getting P0128 errors, there could be something wrong with your engine control unit. This is usually caused by an internal short circuit somewhere in the electrical component.
A car with an intermittent heating problem may be caused by a faulty connection in the wiring or at one of the connectors that your ambient temperature sensor plugs into. Another possibility is that there's debris blocking the cold air intake sensor inside your air filter box.
Replacing this sensor, however, won't take longer than about half an hour if you take your time and follow the instructions in our guide to replace an ambient temperature sensor. In addition, you won't need any tools other than a wrench and some screwdrivers.
Use our Vehicle Locator service if you need help finding the right part for your car. Just enter your vehicle details, and it will find all of the parts that are guaranteed to fit.
Bad Ambient Temperature Sensor FAQs
This section covers the most frequently asked questions about the bad ambient temperature sensor.
Does the ambient temperature sensor affect the engine?
It doesn't directly impact how your car runs, but it does play an important role in how the vehicle control unit calculates several other readings.
How long does it take to change a bad ambient temperature sensor?
If you follow our DIY guide, this should only take about half an hour at most. This is because you don't have to remove any parts, just bolts and wiring connectors.
How will a fault in the ambient temperature sensor affect my car?
You'll probably notice that your car starts running hot when it should be heating up, even if it's a chilly day out. This can lead to all kinds of problems with your fuel economy and engine performance, so you must have this taken care of as quickly as possible.
How does the engine control unit calculate the ambient temperature?
The computer measures the voltage output from your cold air intake sensor, generating a digital readout for you on your dashboard display. This way, you know exactly what's going on with your car's engine temperature any time you drive it.
Does ambient air temp sensor affect AC?
No, the ambient air temperature sensor only impacts how your engine works and vice versa. The AC unit is separate from this part of your car's functionality.
Does a bad ambient air temp sensor cause a check engine light?
If you have a P0128 error code, the ambient air intake temperature sensor has likely gone bad. Your mechanic will be able to confirm this for you, though it should only take about an hour to replace this part if you follow our guide.
What's the difference between ambient temperature and intake temperature?
The intake temperature is the reading that your car control unit calculates using your cold air intake sensor information. In contrast, the ambient air intake temperature is the actual air outside your car.
Can you reset a check engine light caused by an ambient temp sensor?
Unfortunately, no. To get rid of the P0128 error code that means bad ambient air intake temperature sensor on your car's dashboard, you'll need to have it replaced with a new one.
How long does it take for this error to appear?
The P0128 is a generic diagnostic code that your car control unit will produce if the ambient air intake temperature sensor goes bad. Unfortunately, the vehicle control unit produces this error as soon as it's made, so you'll need to have the part replaced promptly, or you might experience serious fuel economy and engine performance problems.
Can a bad ambient temperature sensor affect your evap emissions?
Yes, because the computer will also use this sensor to determine the amount of fuel vapor released by your gas cap as you fill up your tank. If it can't detect any vapor coming from the gas cap, that means you have a vacuum leak, and it won't be able to calculate your fuel economy accurately.
Can a bad ambient temperature cause a stalling problem?
Yes, if the engine control unit misinterprets the erroneous data coming from your ambient air intake sensor, you'll likely have a hard time starting up your car and maintaining consistent RPMs as you drive, even on flat roads.
How do you know if your ambient air temperature sensor needs to be replaced?
You'll need to have it checked by a mechanic, but the P0128 error code that appears on your car's dashboard display is very likely to indicate that this part of your vehicle has gone bad.
What happens when you drive with a bad ambient air intake temperature sensor?
Your car's powertrain control unit will either misread the erroneous data coming from your cold air intake sensor, or it won't be able to detect any signal at all, so you might notice that your engine is running too hot. Either way, this can lead to serious fuel economy and engine performance problems if left unrepaired.
What should you do if your check engine light comes on?
If you get a P0128 error code, it means that the ambient air intake temperature sensor has gone bad and needs to be replaced. To fix this problem, keep reading our guide for step-by-step instructions on how to replace the part yourself or take your car to a certified mechanic for help.
How much does it cost to fix an ambient air temperature sensor?
The cost of a new ambient air intake temperature sensor can vary from $60-$120, depending on where you get it for your car. It will usually take about an hour to complete the replacement, though make sure to check our guide for step-by-step instructions and tips as well as professional advice on how to save money on this project.
If you experience any of the symptoms outlined in this blog post, it may be time to replace your car's ambient air intake temperature sensor. You can find more information on diagnosing and fixing a bad ambient temp sensor by following our guide here. If all else fails, don't hesitate to contact an experienced mechanic for help!