A car’s ECU is responsible for several important tasks, so if it starts to malfunction, you’ll likely notice changes in how your car performs.
The most common symptoms of a bad ECU include car not starting, poor engine performance, engine misfiring or stalling, bad gas mileage, rough or irregular shifting, and check engine light illumination.
In this article, we’ll examine these symptoms and how to test ECU with a multimeter. Knowing the said symptoms will enable us to guess what and where malfunctions happen so that we may go for timely repair.
However, if you want to read bad ECU signals like an expert, you must know first what an ECU is and how does it function? Therefore, we’ll start by focusing on ECU and its function so that you can relate to the malfunctioning ECU symptoms fast.
What is an ECU and how crucial it is?
The engine control unit (ECU), also referred to as engine control module (ECM) or powertrain control module (PCM), is a crucial component of every modern vehicle. The engine control unit is the brain of a car.
The engine control unit is referred to as a car computer because it controls virtually all system operations. It collects information from various car sensors to regulate system operations and offer a high-performance and seamless driving experience.
The power control module plays an essential role in modern cars, where system operations are electronically controlled.
Since various car sensors report the functionality of different vehicle components to the ECU, if it fails, the vehicle will project several drivability and performance issues.
Symptoms Of A Bad ECU
The most common symptoms of a bad engine control unit (ECU) often resemble other engine-related issues.
You may see the Check Engine Light turn on, experience engine stalling, or notice reduced performance and higher fuel consumption. In some cases, the engine may run rough at idle or have trouble starting.
Here’s a closer look at the most common signs of a failing engine control unit and what they mean for your vehicle.
#1. Check Engine Light.
When a problem occurs with the ECU, you can count on the Check Engine Light to illuminate. Yet, this problem alone doesn’t indicate a issue with the computer. Any fault with the major automotive systems can cause this light to come on.
With around 11,000 trouble code definitions, you know that many faults lead to warning lights.
For that reason, we recommend having an advanced code scanner and referencing our DTC library to determine what’s causing the light to come on before making any assumptions.
#2. Stalling Engine.
Before or after the light goes on, you may also notice the engine start to struggle. It can misfire or stall if it gets bad enough. These issues can occur randomly or in a pattern, but these are problems that also mean other things could be wrong.
If the engine control module doesn’t read the information correctly and starts sending out false data, the various systems will try to overcompensate for these malfunctions, leading to a rough ride. The issues can also get worse over time.
#3. Poor Fuel Economy.
To ensure proper combustion, there must be a good balance between air and fuel. When the ECM starts to fail, these readings won’t be understood, so the balance can be off. What happens, as a result, is too much fuel is injected for combustion.
The condition is known as running rich. Because of this added fuel, you are going to spend more at the pump.
#4. Low Engine Performance.
On the other hand, the opposite can also occur. If the ECM keeps the fuel from getting to the combustion chamber, it will feel like the car is starving. When you push on the gas pedal, it could take some extra time before the vehicle starts to respond.
As you put an added load on the car, such as when you try to climb a hill or you are towing, you may notice even more performance issues. It’s not uncommon for the vehicle to vibrate or shake when it’s pushed too hard.
#5. Rough Idle.
A lack of fuel also increases the chances of dealing with a rough idle. A normal car idle is normally between 600 and 1,000 RPMs. If you notice yours isn’t within that range, it’s clear there is a problem with either the engine, ECM or other vital components.
In some instances, the rough idle can get so bad that it feels like the engine might stall. If the car stalls in the middle of traffic and you experience the next symptom, you may be in danger.
#6. Car Won’t Start.
The worst possible problem is that your car won’t start at all. Depending on the severity of the defect, you may only notice a small stumble when initially starting up, but the problem may get worse over time.
There’s also the chance that if the ECM fails, the vehicle stops running with no warning. Without the computer to guide how the vehicle starts, it won’t know what to do. Therefore, you may be able to crank the engine, but nothing happens after that.
As with all of these symptoms, you can’t determine that the ECU is bad based on any of these indications. They are all symptoms of a multitude of other problems.
Common Causes of ECU Failure
ECU problems can develop for many reasons. These are the most common:
- Water or Moisture Damage: Water entering the ECU housing can cause corrosion and short circuits. This is one of the fastest ways an ECU fails.
- Failed Sensors: A bad sensor can send wrong data that damages the ECU over time. Oxygen sensors, MAP sensors, and throttle sensors often trigger ECU trouble.
- Electrical Surges: A faulty alternator, weak battery, or bad wiring can lead to voltage spikes that damage internal ECU circuits.
- Corrosion or Loose Connections: Heat, vibration, and moisture cause wires and connectors to loosen. This interrupts signal flow and leads to ECU malfunction.
- Software Corruption: ECU software can stop working correctly after improper programming or unstable voltage during updates.
- Age and Wear: Over time, heat cycles and long mileage can weaken ECU components.
How To Diagnose Bad ECU Symptoms?
Visual inspection and scanner is the least invasive method to check ECM computers. With a scanner, the engine codes can be deduced which will give a rough answer to why your vehicle is being odd.
There are also a few other ways to inspect the ECU of your vehicle, including checking the battery, a basic swap, and the elimination method. You can even use a multimeter to check the ECU.
Following these ways, you can examine the ECM computer. For purposes of keeping this simple to understand, we will discuss three methods in total.
#1. OBD Or OBD-II Code Scanner.
Every car owner should know what an OBD scanner is, even if they don’t own one. An Onboard Diagnostic (OBD) code scanner can be used to access car data.
This tool helps to check the vehicle’s engine and detect all possible glitches in it. Although not mandatory, we highly recommend you buy an OBD scanner.
For this first technique to testing a car computer, you need an OBD or OBD-II scanner tool. Attach the OBD-II scanner tool to your car’s diagnostic part – this will act as the bridge between your vehicle’s problems and you.
When an OBD or OBD-II scanner displays codes, you have to identify those codes to repair the problems. Try this video for more info.
These are some of the common codes associated with a faulty ECU.
P0600 Code: According to this code, there is an issue with one of the sensors linked to the ECM. Alternatively, a wiring error can be the culprit.
P0700 Code: If you see this code, know there is a problem with the TCM. When a TCM goes bad, it displays similar symptoms to that of a faulty ECM.
P0606 Code: This code is stored in your vehicle when there is an issue with your car’s PCM. A lot of the signs are similar to an ECM’s but they are only somewhat connected.
#2. Visual Inspection.
You have to perform a visual inspection on the ECM computer to test this part. The first thing that you will see when you begin a visual inspection is PINs.
If you see the PINs are intact and good, you can move on to the second step, which is performing a little smell test on your ECU. Understand something is wrong with the ECU if there is a burnt plastic smell coming from it.
For further visual inspection, however, you may have to dismantle the ECU. Try to remain careful during this step and don’t hurry.
After you take apart the car computer board, you have to look for any broken or corroded components in it. If there are any, you have to get them replaced.
#3. Car Battery Check.
You can rely on your battery voltage to tell you if your ECU computer is functional or not. The sensors linked to the ECU cannot perform the right adjustments if the battery voltage isn’t just right. The battery of a car has to be fully charged when you take it out for a spin.
Use a multimeter to check the car battery voltage. Do it in two conditions – once with the engine on and once with the engine off. If the reading is 13.7 volts when the engine is on and 12.6 volts when the engine is off, your battery is charged fully and in good shape.
If the reading is under 12.6 volts when the engine is off and under or over 13.7 volts when the engine is operating, the battery has to be recharged. Make sure to test it again with a multimeter after that.
How To Repair A Faulty ECU?
Fixing or repairing a bad engine control unit can be daunting if you do not possess adequate knowledge about the component or do not have prior experience handling car parts.
And fixing a bad ECU is anything but easy. Without the proper tools and technical know-how, you can very easily mess up the interior of your vehicle.
Warning: Do not try to fix the ECU of your car if you’re a newbie to car repair. Leave the task to a professional if you want the job done correctly.
Here are a few methods to try when attempting to repair a bad ECU:
#1. Ignition Coils.
The ignition coils of a vehicle transform battery voltage across the entire car’s electric system from the ignition system of the car. If the ECU in your car is bad, you must inspect the ignition coil to repair or replace it.
#2. Check For Bad Spark Plugs.
Bad spark plugs may need to be repaired or changed when the ECU in your car is malfunctioning.
#3. Test Fuel Injection.
In case your vehicle is showing bad ECU symptoms, test the fuel injection properly.
#4. Examine Mass Air Flow.
Check out your vehicle’s mass airflow sensor. Make sure this component is working properly.
#5. Fix Throttle Position Sensor (TPS).
A vehicle’s TPS, or throttle position sensor, is directly linked to the engine control unit. Thus, if there is anything wrong with the ECU, it also affects the throttle position sensor.
#6. Idle Air Control Valves.
Also termed IAC, the idle air control valves have to be looked into when the ECU isn’t working. Poor IACs may be preventing the component from functioning.
#7. Test Grounds.
Use a multimeter to test the ground – this is the best way. As mentioned earlier, fixing a bad ECU isn’t simple.
No matter how long you’ve owned a car, you need to have a certain level of experience and knowledge to repair a faulty ECU. This is why we always suggest going to a mechanic when in doubt. Why risk pricier repairs in the future?
How much does ECU cost?
If after diagnosis and you discover the ECU is bad, you’ll either repair or replace it. The cost of the ECU depends on your vehicle’s make and model.
The newer and more luxurious a car is, the more costly the engine control unit will be. It is like purchasing a high-performance car from Mercedes or BMW versus a budget car from the Toyota lineup.
On average, a new ECU will cost around $800 and $200 for installation and programming, making it $1000 for parts and installation. This excludes taxes and shipping fees.
However, the price of engine control units on budget cars can be as low as $400 and as high as $2000 on luxury cars.
FAQs.
Q: How do I test my ECU?
If you think your ECU is bad and it causes your problems, follow these steps to properly diagnose it. First, you’ll need to do a visual inspection, or you can try a swap, and last, you can always use an OBD11 scanner.
Visual route
When going through the visual route, uninstall the ECU from the car and remove the cover and inspect the circuit points. If you see water-damaged ECU signs, or you notice burnt components, it shows you have a faulty ECU.
Swapping route
If you couldn’t figure out a bad ECU via the visual route, try swapping it. This works best for older cars where programming is not a factor. But in newer cars, you can sometimes do a swap as well.
For example, if you find another ECU with the exact part number, you can insert it into your car. If the vehicle regains communication, that shows the ECU is bad and needs replacement.
Using OBDII scanner
Sometimes, you can use an OBDII scanner on the vehicle, and the engine control module will self-diagnose itself to be damaged. That shows you need a replacement.
Q: How much is an ECU tune?
ECU tuning or flash tuning, as it’s popularly called, is an effective way of maximizing overall vehicle operation by at least 30℅. But how much does it cost to tune an engine control unit?
The cost of tuning an ECU heavily depends on the vehicle’s make and model. However, professional tuning costs between $200 to $700.
Q: Can an ECU overheat?
Of course, an engine control unit can overheat and cause it to malfunction. A problem with the engine control module spells a malfunction with your engine system components.
When the ECU overheats, it’ll enter ‘limp mode, which means it’ll limit the engine power. It’ll also trigger the check engine light to notify the driver of an imminent problem in the system.
Q: Can I put a used ECU in my car?
Yes, you can swap an ECU from one vehicle to another. But you’ll have to reprogram it, which requires a programming device, a laptop, and access to the vehicle manufacturer’s website.
Depending on the make and model of your vehicle, programming an ECU may require the following:
- Using diagnostic tools to program it
- Involve swapping articles from the internal memory of the old ECU to the Used one you’re replacing it with.
The latter isn’t a simple job for an average mechanic. You’ll need to take the vehicle to an ASE-certified mechanic or a dealership.
Q: Can ECU cause misfires?
A malfunctioning engine control unit will project several symptoms such as a check engine light illumination, poor gas mileage, and engine misfire, among others.
Many factors can cause an engine to misfire, but if the engine stalls erratically and misfires, a bad ECU is a culprit.
If there’s no pattern to the severity or frequency of the misfire and it comes and goes with no pattern, checks the ECU.
Q: Can you bypass the ECU?
Practically, no. Mechanics can bypass the ECU during some system tests and diagnoses; it requires harnesses, breakout boxes, and specialized scanners. But the ECU must be present for a car to run.
Final words
The ECU plays a crucial role in system operation and controls the overall functionality of the vehicle. Any issues with it will affect the efficiency of car sensors and other components that report to it.
Engine control units on newer vehicles are quite sophisticated and complex. For this reason, they’re quite challenging to diagnose.
If you notice two or more of the symptoms of a bad ECU listed above, fix it as soon as possible before it escalates to a major repair job.