“What sensors can cause a car not to start?” is a very relevant question, given that many modern cars are controlled by sensors from start to finish. These sensors send signals to the vehicle’s brain (ECU), which interprets the signals and uses the info to control the vehicle.
Interestingly, there are several sensors that, if they malfunction, can delay or prevent a car from starting. This article will discuss these sensors and suggest ways to fix them if they malfunction.
JUMP TO TOPIC
- 1 What Sensors Can Stop a Car from Starting?
- 1.1 A Broken Mass Air Flow Sensor
- 1.2 A Faulty Crankshaft Position Sensor
- 1.3 A Damaged Oil Pressure Sensor
- 1.4 A Faulty Throttle Position Sensor
- 1.5 A Faulty Fuel Pressure Sensor
- 1.6 A Faulty Camshaft Position (CMP) Sensor
- 1.7 A Broken Oxygen Sensor
- 1.8 A Malfunctioning Coolant Temperature Sensor
- 1.9 A Damaged Anti-lock Braking System Sensor
- 1.10 The Manifold Absolute Pressure (MAP) Sensor
- 2 How To Fix Sensors That Prevent a Car from Starting?
- 3 Frequently Asked Questions
- 4 Conclusion
What Sensors Can Stop a Car from Starting?
The following sensors can stop a car from starting: mass air flow sensor, crankshaft position sensor, oil pressure sensor, throttle position sensor and fuel pressure sensor. The rest are camshaft position sensor, oxygen sensor, coolant temperature sensor, anti-lock braking system sensors and manifold absolute pressure sensor.
A Broken Mass Air Flow Sensor
The mass airflow sensor (MAF) monitors the volume of air going into the engine via the air filter and reports it to the engine control unit (ECU). The ECU then uses the signals from the MAF to calculate the amount of fuel to pump into the combustion chamber.
It then signals the fuel pump to spray gas into the chamber and instructs the ignition to burn the mixture. Now, if the MAF malfunctions, it won’t send the right signals to the ECU; thus, the ECU can’t instruct the pumps to send some gas for combustion.
When that happens, the car will experience starting problems as there’s no air or fuel in the combustion chamber. In modern vehicles, the ECU reverts to default values if the MAF functions, allowing the fuel pumps to send fuel into the chamber.
However, the fuel pumps end up spraying more or less fuel than needed, leading to a rich or lean combustion. Both situations can destroy the car engine, which is why you should repair the MAF when it becomes faulty.
A Faulty Crankshaft Position Sensor
The sensor checks the position and measures the rotational speed of the crankshaft, which it relays to the ECU. The ECU then uses the information to start the engine by igniting the air-fuel mixture in the combustion chamber. When the sensor becomes faulty, it can’t relay the crankshaft’s position and rotational speed to the computer. Thus, the computer can’t ignite the air-fuel mixture to produce enough power to start and keep the car running.
A Damaged Oil Pressure Sensor
The oil pressure sensor monitors the oil pressure and sends the information to the car’s computer. The computer then uses that information to determine how to lubricate the moving parts of the engine. Thus, if the oil pressure drops below the required level, the sensor sends the information to the ECU, which protects the engine by reducing its power.
When it becomes faulty, the computer might receive incorrect signals and interpret it as a dangerous situation. This would cause the computer to shut down as a precautionary measure because starting an engine on an extremely low oil pressure can cause damage.
A Faulty Throttle Position Sensor
The throttle position sensor (TPS) tracks the movement of the throttle body and communicates to the control unit. When a driver presses the accelerator, the throttle valve opens. The sensor then informs the ECU of how wide the valve is opened. The ECU then uses that information to calculate the volume of air that can flow into the intake manifold for combustion.
A faulty TPS might send wrong signals to the computer, forcing it to allow too much or too little air, which might affect combustion. When combustion is affected, the engine might not start or have troubles that could lead to a breakdown.
A Faulty Fuel Pressure Sensor
A fuel pressure sensor senses the flow of pressure in the fuel line and informs the ECU. The computer then uses those signals to determine the fuel delivery into the engine. The ECU also uses that information, as well as signals from the MAF sensor, to determine the precise amount of fuel needed for proper combustion. If the fuel pressure sensor develops a fault, the engine won’t start because the ECU doesn’t know the right amount of fuel to send for combustion.
Thus, the ECU might not instruct the fuel injector to send fuel into the chamber for combustion, robbing the engine of its ability to start. Even if it starts, the pressure from the fuel supply might be so low that the engine will shut off soon.
A Faulty Camshaft Position (CMP) Sensor
The CMP sensor tracks the position of the camshaft and its rotational speed. It then relays the information to the computer, which uses it to regulate the opening and closing of the engine valves for combustion.
The ECU also uses the information to regulate other engine functions, such as ignition and fuel injection timing. Thus, a faulty camshaft position might affect various functions of the engine, preventing the car from starting.
A Broken Oxygen Sensor
A broken oxygen sensor might stop a car from starting due to its vital function in the engine. The oxygen sensors enable the ECU to calculate the amount of air for combustion by checking the level of oxygen in the exhaust gasses.
When the sensor is faulty, the ECU might not know the amount of air to supply for complete combustion. This will affect the engine’s performance as the energy from the combustion chamber won’t start the vehicle.
A Malfunctioning Coolant Temperature Sensor
A coolant temperature sensor monitors the temperature of the engine, enabling the ECU to calculate the air-fuel mixture. For example, during cold engine cranks, the air-fuel mixture needs to be rich (more fuel than air) to aid engine start. Thus, the coolant temperature sensor informs the ECU that the engine is cold, and the computer adjusts the air-fuel ratio for rich combustion.
However, when the sensor develops a fault, it might send wrong values to the ECU, causing the computer to calculate the air-fuel ratio wrongly. As in the example above, the sensor might cause the ECU to signal a lean combustion during a cold start. When that happens, the vehicle might struggle to start or not start at all.
A Damaged Anti-lock Braking System Sensor
Many modern cars have sensors installed on the wheels to track their speed and transmit it to the ECU. Thus, when one wheel loses traction, the sensor alerts the computer, which transfers more power to the wheel with more traction. This prevents the car from skidding or slipping on slippery surfaces.
Though the anti-lock braking system sensor can’t directly stop a car from starting, it can trigger other components and sensors. The ABS sensor is a part of the electronic system and a component of several electronic control modules. Therefore, if it develops a fault, it won’t send the right signals to some of these modules that aid in the starting of the engine.
The Manifold Absolute Pressure (MAP) Sensor
The manifold absolute pressure sensor monitors the pressure in the air intake manifold and reports to the ECU. The computer then decodes the report and uses it to regulate the ignition timing, adjust the air-fuel mixture, and control the fuel delivery system, among other activities.
A faulty MAP sensor may send inaccurate results to the ECU, causing it to incorrectly adjust the air-fuel mixture. Thus, the car won’t start because the combustion doesn’t produce enough power to get the vehicle going.
How To Fix Sensors That Prevent a Car from Starting?
To fix sensors that prevent a car from starting, start by identifying the problem and the sensor causing it. Next, gather information about that particular sensor and either fix it or replace it. Some sensors may only be dirty and may need cleaning to get them working again.
Identify the Sensor Causing the Problem
As we’ve demonstrated in this article, many sensors can prevent the vehicle from starting; therefore, it’s important to identify the problematic one. Identifying the culprit includes running some tests on suspected sensors until you get the main cause.
Note that these tests differ from sensor to sensor; thus, you need to check the car manual to know how to test each of them. If you can’t lay your hands on one, you can browse the internet for articles on how to test each sensor.
Instead of going through the hustle of testing each sensor until you detect the faulty one, you can use an OBDII Scanner. The OBDII Scanner can scan the entire vehicle and identify the sensor using codes. You can then use a catalog to decipher the codes and locate the source of the problem.
Gather Enough Information About the Sensor
Once you’ve discovered the culprit, gather as much information as you can on the sensor. Check the location of the sensor, its functions and the wires connected to it. Also, look up the type of sensor made for the car’s model and ensure you purchase the same type to make the car start.
Reset, Replace or Clean a Sensor
Locating and testing the sensor
will determine whether it needs to be reset, replaced or cleaned. Resetting a sensor is easier and quicker than cleaning or replacing it. For example, on how to reset a crankshaft position sensor no start, all you do is to start the car and turn off all accessories. Next, accelerate the vehicle until you reach 55 mph and maintain the speed for about 5 – 6 minutes.
However, don’t make the mistake of starting a car with a faulty crankshaft sensor. Contact a mechanic to guide you on how to start a car with a bad crankshaft sensor to enable you to drive to the shop to fix the problem.
Frequently Asked Questions
Why Is Your Car Cranking But Not Starting?
The reasons your car is cranking but not starting have many root causes. It could be due to bad sensors, a poor fuel delivery system, ignition coil problems, a dead battery, or low fuel. Other causes could be faulty electrical systems, damaged exhaust systems, or engine problems.
Sometimes, the ECU may be faulty, or the ECMs in the vehicle may be dirty. You’ll need a specialist to help you diagnose the exact cause of the problem and help you rectify it.
Conclusion
In this article, we’ve discussed what sensors can cause a car not to start after trying to turn on the engine.
Here’s a recap of all that we’ve discovered:
- The sensors that cause a car not to start are the MAF sensor, crankshaft position sensor, oil pressure sensor, TPS and fuel pressure sensor.
- The others are camshaft sensor, oxygen sensor, coolant temperature sensor, anti-lock braking system sensor and manifold absolute pressure sensor.
- Most of these sensors play a part in the combustion process; thus, they can give the engine the requisite power to start up the car.
- To fix the problem, you need to identify the sensor by locating and testing it, or you can use an OBD II scanner to pinpoint the source of the issue.
You can then decide to clean, fix, or replace the sensor based on your assessment or tests. Car sensors are delicate and complicated; thus, we recommend that you allow a mechanic to check and fix them for you.
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