(Updated on June 30, 2020)
The ECU is the engine control unit of your vehicle. It is also often referred to as the PCM (powertrain control module) or ECM (engine control module).
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 are the most dependent on the ECU.
Through a numerous array of electronic sensors, chips, and components within the vehicle, the ECU can transmit data feedback to the engine. The nature of this feedback will determine which function the engine will perform next.
This helps a great deal with calculating the proper amount of air and fuel needed for the internal combustion process. That way, better fuel efficiency can be achieved.
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 many noticeable symptoms would present themselves. It wouldn’t take you long to realize the ECU was responsible.
However, what you may wonder about is why the ECU malfunctioned in the first place. There are lots of internal causes which could contribute toward this. Below are the top 5 causes of a bad ECU. Investigate them as soon as you notice problems with the ECU.
Read also: Car Immobilizer: Basic Function and Bad Symptoms
1) Dead Battery
Car batteries have electronic cells which need to function in order for the ECU to function. If any of the cells in your car battery are dead, then your ECU is going to fail soon afterward. Once all the cells are dead, the battery is considered dead and your entire vehicle won’t be able to function.
You won’t be able to even start your vehicle and get the engine running. So, look out for the early warning signs of a malfunctioning ECU and then have your battery examined right away.
2) Corrosion
The ECU has seals around it which are supposed to prevent moisture from entering inside. However, after a number of years, these seals tend to become worn out. If the seals become too worn, it will be easier for moisture to pass through them and enter the ECU.
Moisture is a bad thing to have in an ECU because corrosion will form on its components. If the corrosion is not cleaned away quickly, it will cause these components to get damaged. Then you will have a malfunctioning ECU.
Related: How to Clean Corroded Battery Terminals
3) Low Voltage
The average ECU is expected to have at least 9 volts, but preferably 12 volts. There is wiring that runs into the harness of the ECU where you can check the voltage amount.
All you need to do is connect a voltmeter gauge to it. This device will be able to detect how much voltage is running through the ECU. If the voltage is 6 or less, then this is likely causing your ECU problems.
4) Bad Jump Starting
Whenever a jump start is performed on your battery, you need to ensure that the jumper cables are attached properly. If you attempt to jump start your vehicle with the cables attached incorrectly, then it could short out your ECU by causing it to spike too quickly.
This will require you to get the ECU repaired or possibly even replaced. This can end up costing thousands of dollars in expenses.
5) Bad Starter
Many vehicles have starters with their own sensors in them. One of these sensors is the override sensor which manages how many volts the ECU will receive.
If this sensor were to go bad, then the ECU would not receive the correct amount of voltage. Then it would malfunction and cause further problems in your vehicle.
Another problem that could happen is if you replace your starter motor with a new starter that is not compatible with your vehicle’s ECU. Make sure any new starter that you purchase has the right sensors which can communicate with the ECU properly.
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.