The ECU is the Engine Control Unit of your vehicle. It’s also commonly referred to as the ECM (Engine Control Module) or even a PCM (Powertrain Control Module), although a PCM has additional functions as well.
This electronic module is a built-in computer which your vehicle depends on for managing a variety of its systems and functions. Think of it as the vehicle’s brain. The engine and drivetrain depend heavily on the ECU.
Using numerous electronic sensors, chips, and components within the vehicle, the ECU can transmit data feedback to the engine. This feedback determines which function the engine will perform next.
This process is essential for calculating the correct amount of air and fuel needed for internal combustion. As a result, the vehicle can achieve better fuel efficiency.
Read also: Car Immobilizer: Basic Function and Bad Symptoms
Common Reasons for ECU Problems
The ECU regulates virtually every important system and function in your vehicle. If you were to ever have a bad ECU, then quite a few noticeable symptoms would present themselves. It wouldn’t take you long to realize the ECU was responsible.
But why does an ECU fail in the first place? There are many internal factors that can contribute to its malfunction. Here are the most likely causes of a faulty ECU:
1) Dead Battery
Car batteries have electronic cells that need to function for the ECU to work properly. If any cells in your car battery die, your ECU will soon fail. Once all the cells are dead, the battery is considered dead, and your entire vehicle won’t function.
You won’t be able to start your vehicle or run the engine. So, watch for early warning signs of a malfunctioning ECU and have your battery examined promptly.
2) Corrosion
The ECU has seals around it to prevent moisture from entering. However, after several years, these seals can wear out. If the seals become too worn, moisture can more easily pass through them and enter the ECU.
Moisture inside an ECU (or any other electronic component) is problematic because it leads to corrosion on its components. If the corrosion isn’t cleaned away quickly, it will damage these components, resulting in a malfunctioning ECU.
Related: How to Clean Corroded Battery Terminals
3) Low Voltage
Most modern ECUs are designed to operate within a specific voltage range, typically between 9 and 16 volts, with 12 to 14 volts being optimal. You can check the voltage by connecting a voltmeter to the wiring that runs into the ECU’s harness.
This device will detect how much voltage is running through the ECU. If the voltage consistently falls below 9 volts or fluctuates erratically, this is likely causing your ECU problems. Prolonged exposure to low voltage can lead to erratic behavior or failure of the ECU.
While an ECU might still function at lower voltages, it may not operate correctly or reliably. This can lead to various issues with engine performance and other vehicle systems.
4) Incorrect Jump Starting
When jump-starting your battery, make sure to attach the jumper cables correctly. If you attempt to jump-start your vehicle with the cables attached incorrectly, it could short out your ECU by causing a sudden voltage spike.
This situation will require ECU repair or possibly even replacement, which can cost thousands of dollars.
5) Bad Starter
Many vehicles have starters with their own sensors. One of these is the override sensor, which manages how many volts the ECU receives.
If this sensor fails, the ECU won’t receive the correct voltage. This will cause it to malfunction and lead to further problems in your vehicle.
Another issue can arise if you replace your starter motor with a new one that’s incompatible with your vehicle’s ECU. Make sure any new starter that you purchase has the right sensors to communicate properly with the ECU.
6) Electrical System Overload
The ECU is part of a complex electrical network in modern vehicles. Power surges from other components or aftermarket accessories can potentially overload and damage the ECU. This is particularly common when installing high-powered audio systems or other electrical upgrades without properly accounting for the increased power demand.
To avoid this, don’t attempt any aftermarket installations if you’re not 100% confident in your abilities. For most individuals, it’s best to leave audio upgrades to the professionals.
7) Software Issues and Chip Tuning
Modern ECUs rely heavily on software to control various vehicle functions. Software glitches, corrupted data, or failed updates can cause ECU malfunctions or even complete failure (bricking). Additionally, chip tuning or ECU remapping, while popular for increasing performance, introduces additional risks if not done properly.
Chip tuning involves modifying the ECU’s software to alter engine parameters like fuel injection timing, boost pressure, and rev limits. While this can increase power output and efficiency, it can also stress engine components beyond their design limits.
Poorly executed remapping can lead to engine damage, increased emissions, and in most cases, voided warranties. On top of that, some remapped ECUs may become unstable or fail completely and your car manufacturer is not going to bail you out.
If considering chip tuning, it’s crucial to use reputable tuners and understand the potential risks. If still under the original vehicle warranty, it’s usually best to wait until you are out of coverage. In almost every case, the dealership can quickly determine whether your vehicle has been “chipped” and will in most cases, not cover any future warranty work.
If you still insist of a chip tune, be sure to keep a backup of the original ECU software and be prepared for the possibility that remapping could lead to ECU issues down the line.
8) Manufacturing Defects
While relatively rare, there’s always a small chance that an ECU may have inherent flaws from the factory that leads to premature failure. These defects can range from faulty components to improper assembly.
In some cases, manufacturers may issue recalls for known ECU problems. That’s why it’s important to register your vehicle to stay informed about any recalls or technical service bulletins for your vehicle.
If you or your mechanic suspects a manufacturing defect, document all symptoms and consult with your dealership. They may be able to provide repairs or replacements under warranty, even if the standard warranty period has expired.
Diagnosing ECU Failure (Step-by-Step)
Step 1. Check the Check Engine Light
Look at your dashboard when you start the car. The Check Engine Light (CEL) should briefly illuminate and then go out. If it stays on, it may indicate an ECU problem, though it could also signal other issues.
A constantly lit or flashing CEL requires further investigation. Note that in some ECU failures, the light might not come on at all.
Step 2. Use an OBD-II Scanner
Plug an OBD-II scanner into your car’s diagnostic port, typically located under the dashboard on the driver’s side. Turn the ignition on without starting the engine, then follow the scanner’s instructions to read error codes.
Look for codes starting with “P06,” as these often relate to ECU issues. Examples include:
- P0600: Serial Communication Link Malfunction
- P0606: ECM/PCM Processor Fault
- P0607: Control Module Performance
Write down any codes you find. Even if they don’t start with P06, they could provide clues about what’s affecting your ECU.
Step 3. Inspect Battery and Connections
Check your car’s battery and its connections. Look for signs of damage on the battery itself (such as cracks or bulges) and check the terminals for corrosion (a white, green, or blue powdery substance).
If any corrosion atop the battery exists, clean it following our instructions. Confirm that all connections are tight, both at the battery and where cables connect to the car.
A weak battery or poor connections can mimic ECU problems, so addressing these issues may solve the problem.
Step 4. Test Battery Voltage
Use a multimeter to check your battery’s voltage. It should read 12.4-12.7 volts with the engine off, and 13.7-14.7 volts when running.
Any reading outside these ranges may indicate charging system problems that could be affecting the ECU. Low voltage can cause ECU malfunction, while high voltage might damage it.
Step 5. Check Fuses and Relays
Find your car’s fuse box and inspect fuses related to the ECU. Replace any fuse that’s blown and check/test relays connected to the ECU.
Faulty fuses or relays can disrupt power supply, causing symptoms very similar to ECU failure. Consult your owner’s manual to locate the correct fuses and relays if you’re not sure where to look.
Step 6. Look for Visible Damage
Visually inspect the ECU and its wiring harness. The ECU is normally under the dashboard or in the engine bay but may also be located elsewhere, like under the center console. If your owner’s manual doesn’t specify the location, you may need to search online or purchase a vehicle-specific service manual (a great investment if you plan on doing any car maintenance or repair).
Look for signs of physical damage, water intrusion, or heat damage. Check for corroded connections or frayed wires. Any visible damage could explain ECU malfunction and will likely require professional repair or replacement.
Step 7. Monitor Engine Performance
Observe how your engine runs. Notice any rough idling, stalling, misfire, or sudden changed in fuel efficiency? Any of these can indicate ECU problems (among other things).
Keep track of any unusual behavior, especially if it coincides with other symptoms. Persistent performance issues, particularly after addressing other potential causes, may point to an ECU issue.
Step 8. Test Sensor Inputs
Use a multimeter to test various sensor inputs to the ECU, such as the MAF sensor or O2 sensor. These types of faulty sensors can imitate ECU failure symptoms.
Again, consult a service manual or online source for proper testing procedures and expected readings. If sensor readings are off, replacing the sensor might solve the problem without needing to address the ECU itself.
Step 9. Perform a Voltage Drop Test
Check for voltage drops across the ECU’s power and ground connections using a multimeter. Significant drops can indicate wiring problems affecting ECU performance.
This test requires some technical knowledge, so consider getting help if you’re unsure if this process.
Step 10. Consult a Professional
If you’ve completed all the steps above and still suspect ECU failure, it’s time to consult a professional mechanic or dealership. They have advanced diagnostic tools and expertise to pinpoint ECU issues definitively.
A technician can perform more complex tests and determine whether the ECU needs repair or replacement, or if the problem is completely unrelated.
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hello i have a problem with my ride polo 6r gti 1.8 2016 is giving a problem when am driving is goes well but when am stopping it epc,scu light comes on and start to idler bad ref is high and then it switched off itself
I have a 2008 Dodge charger pursuit it seems like the ecu becomes disconnected on the first plug top if the power gets disconnected. If I turn on the key and wiggle the wire you can hear the fuel pump kickoff and you know it’s connected. Then the car will start is this a bad computer or connection?
I don’t know. I’m inclined to think it’s a bad connection. Do you see any corrosion or damage to the main harness that connects to the ECU?
If you can find another ECU it wouldn’t hurt to try swapping them.
I have a 2008 Saturn vue which runs a little rough, car turns off about 20 seconds after pulling out key from ignition and stepping out of the car, steering becomes a bit stiff sometimes, no crank no start sometimes, dashboard malfunctions sometimes, low acceleration performance, AC doesn’t cool anymore. Not sure what the problem is. Could it be a faulty ECM?
Are you saying the car continues to run after removing the key?
hi, sir, i was trying to connect my multimedia CAN decoder to CAN high-low line on OBD port of my toyota, when after some time, all lights (traction, collision, check engine,eco idle and other) started blinking. i removed the connections that i was trying to establish, immediately. also removed battery terminal to reset ecu, but all in vain. these light keep on blinking on dash cluster, although the car starts and ride. But, no AC, wiper, headlight switches work anymore, moreover, headlights turn On automatically, sooner i start car, never get off by switch. i think i have damage some CAN lines. any help in this regard would be highly appreciable. thanks
Hi, I drive a 2011 Audi A4, recently been finding it difficult to start, but 5 seconds with a battery pack and it fires up. Yesterday was such a day, so I used the pack and went on my way. Did 15/20 minutes driving and parked up for 2 hours. Went back to my car and there’s no power. Put the battery pack on, the ignition won’t turn on, but the radio and all lights work.
I did find some corrosion on the battery today (I use the charge ports in the engine bay so I’ve never looked at the battery)
Any suggestions? Jumper cables and my pack are giving me enough power to turn on the radio and lights, but the ignition still won’t turn on.
Clean any corrosion off of the battery and battery cables. If that doesn’t help, how old is your battery? It may be time to replace it.
Hey, thanks for the reply. I cleared the corrosion and ended up replacing the battery, unfortunately it didn’t fix the issue so I’m not sure where to go from here.
I have a 1997 Dodge B3500 chassis/camper van. Crank no start began last spring, I replaced cam and crankshaft sensors, ignition coil, distributor cap/rotor and spark plug wires. I checked as best as I could (I’m not a mechanic) grounds and voltage. I then found an old post that said use a hair dryer on ECM to warm it for 15 minutes, if the car starts the ECM is bad. Sure enough, it started up. I sent ECM out to rebuilt.
Once rebuilt the only code that appeared was faulty oxygen sensor, which was replaced.
Everything was fine for a few months. I went out for supplies for a new camping trip, made several stops, but the last one I experienced crank no start again.
Can you give me any clues where to look next, or what information I might give a mechanic? I use my van for work, I’m an event photographer and looking at the rest of the summer and fall sleeping in a tent. Ugh.
Thanks in advance.
I wonder if your ECU went bad again? Could there be anything that is melting or frying the ECU in that area?
I have a 2004 Lexus es330, the battery drains even after it’s been driven. Once I park overnight, the next morning it’s completely drained. I recently change the ECU and that’s when this started happening.. the alternator is fine.
What else did you disconnect when you changed the ECU?
Hi I have a vw 2lt tdi B7 2011 estate and the check engine light comes on when I check it gives a code Po 40300 it says erg problem
Badly stuck in Ireland – Had to remove blown exhaust manifold off a V8 – 5 out of 6 studs snapped off by the head. I disconnected the battery. I then used another 12 volt battery , connected jump leads to the stud and the engine head to reden the studs so i could get them out. It worked. Got them all out, replaced with new bolts and put it all back together. But now engine will not start. I disconnected all power to the engine before i did this. Is it possible I have blown the ECM even though the battery was disconnected?
Check your main fuse. I doubt it’s the ECM.
i need inf:. on my 1998 plymouth voyger 2.4 ltr 4 cyl plymouth voyager horn wire got cut. some way it destroyed something in the ecm, pcm, or ecu, i fixed the cut horn wire and replaced the ecm, pcm, ecu. it started fine once, but never started again. is there a fix for this problem? your help will be appreciated and a life saver’. (this van is an electric wheel chair lift for an invalid woman with only one leg and has had diabetes ever since she was 7.) please help if you can or know anyone that might know you could ask. sincerest thanks
Hi My Car Toyota Harrier ABS LIGHT , eNGINE LIGHTS , Traction lights , PCS ,ICS LIGHTS on what could be the reasons .
There could be a lot of reasons. Search through forums to see what all of those lights coming on at the same time could mean. You will probably also find specific troubleshooting steps for your vehicle in the factory service manual if you can get your hands on one of those. You can find them online. Search something like “toyota factory service manual” then pick your year, make, and model. Some sites let you enter a VIN instead.
Surely over voltage can also destroy an ECU…? If the voltage regulator is poor, the ECU would suffer. What is the maximum voltage a typical ECU can happily take?
The voltage regulator is typically built into the ECU these days. You probably don’t have to worry about over volting an ECU unless you hook it up to something bigger than a car battery that supplies more than 12V.
My Vezel was giving error codes related to PCM Malfunction, VSA System Malfunction and HV Battery Cell Voltage Sensor Internal Circuit Malfunction. The mechanic told me to replace Hybrid Battery Pack.
But I found that the 12 Volt Battery was performing low, due to which these errors were reporting by the Car.
12 Volt Battery is very important part of Hybrid Car. It has to be in healthy condition, otherwise similar errors can occur.
My 2005 Dodge ram hemi sport will start but stepping on the gas pedal does very little and its running rough but i put the scanner on it and nothing. also i have the other light flashing the performance one not just the check engine light could the ecu be dead or bad ??
The ECU isn’t dead if the truck is running. I’d have a mechanic do a diagnostic on it. There may be a few things you can do to make it run better that will be obvious to them when they take a look at it.
I am having the same problem for over 2 months.
When i start the car in the morning my temp. gauge stays on cold and it does not move at all.Then, i restart the car and temp gauge moves.The error is G62 sensor with implausible signal.
I have changed the sensor and thermostat and i even changed the coolant(flushed out completely).
But the problem remains and my check engine keeps coming back.Is it connector plug or something like that?
Some people say its ECU.But if its ECU how is it possible that it only happens in the morning,after that its fine. It tends to have more problem during cold days.
Has anyone experienced something similar? I am really frustrated. Car is MK6 ,2.OTDI
Hi I have a Ford Escape 2017. my engine computer fell out when I hit a pothole. we reattached it but now the car won’t start. the battery isn’t dead because the car lights and everything still work. what could be a possible solution??
Are you sure it was reattached firmly? Did the computer fall out of the car entirely or just hit the floor?
I have an Accord 09 v6,my car works fine for every first 1hr drive and then it just won’t rev past 3000rpm dropping the speed to 20-30mph and after parked and off the ignition for 1min,it works fine for another 10mins… sometimes the cylinder Misfires and it through an engine code 83-19 ECM/PCM Relation Failure
You might be entering limp mode, which is would limit your engine speed and power. Hard to say why those codes are being thrown, and a diagnostic in person will be needed to help narrow it down for you.
I have a 2013 Cadillac cts, the battery drains even after it’s been driven. could be the stereo or the alarm.
Could be, but you’ll have to do a parasitic draw test to narrow it down.
What could be wrong with my car. The check engine light doesn’t come on when I switch on the ignition. And not until it come on it won’t start. I changed my ECU- with a used one, and it started working fine uptill about 5 months and then goes bad again to the same problem. It can go off anytime and refuses to start. After some times or a day after, the check engine light will come on and then start. Is it the ECU that’s faulty or there is an electrical problem damaging the ECU? I drive a Kia Cerato 2009.
I don’t understand. The vehicle won’t start until the check engine light illuminates?
I wonder if there is a problem getting power to the ECU. Check the wiring leading to the ECU to see if there is any visible damage to the insulation, or anything that may indicate a problem with the power supply going to the ECU. Check your fuses as well.