Modern engines are amazingly complicated devices. They rely on split-second timing and on-the-fly adjustments to create an extremely efficient machine. To control all that, a special device is installed in the engine bay, known as an engine control module (ECM). It manages every component that directly impacts the motor, using an array of sensors and a large database stored in its memory.
A Simple Computer Provides Everything Your Vehicle Needs
The ECM, also known as an electronic control unit (ECU), uses relatively basic electronics by today’s standards. For instance, a smartphone has about 1,000 times the processor speed as the ECM’s microprocessor. Yet, this is plenty of power to do everything it needs to. Within its memory banks, there are thousands of data points that it checks many times a second.
The data is kept in a lookup table which is accessed via a cutting-edge algorithm. This forms a complicated matrix that instantly responds to the constantly changing dynamics inside the engine. It uses the input from the driver to determine if the engine needs more power versus more efficiency. For instance, if you’re pulling a boat and trailer up a steep incline, your engine performance needs to concentrate on torque, whereas if you’re driving at a consistent speed on a flat road, the ECM will provide peak fuel economy.
The ECM Provides Unprecedented Precision
If the ignition timing is off as little as 2 tenths of a second, the vehicle will run poorly. With over 2,000 moving parts in modern engines, everything must be perfectly timed. In the old days, car motors used a distributor to send the spark to each cylinder at the right time. As the vehicle ran faster, it created a stronger vacuum, which would advance the spark.
This worked reasonably well until consumers and government regulations demanded that cars get more than the 10 – 15 miles per gallon they averaged back then. Plus, without intricate control of each moving part, the engine wears out substantially faster compared to a working ECM; it wasn’t unusual to find tiny metal shavings inside used oil back then.
Using the onboard firmware, the electronic control module adjusts the air-fuel mixture to match the power needs. It also works with the transmission control module (TCM) to increase performance while using less gasoline. The idle speed, crankshaft revolutions and variable valve timing all rely on the ECM to keep everything working together. This is part of the engine management system (EMS) that has gradually been improved over the last few decades, and a major reason why cars last, on average, about 3 times longer than they did in the 1980s.
Another benefit of many modern ECMs is that they can be reprogrammed very easily. For instance, vehicles with engine modifications or that are going to be used for specific purposes can have the data lookup tables altered to match the desired performance. There are custom tables available for almost every conceivable purpose.
Signs the ECM May Be Failing
Generally, the ECM should give you many years of good service. However, there are a few problems that can damage – or even destroy – your module. An overvoltage is the most common way it’s harmed. If someone jump-starts your vehicle and connects the jumper cables to the wrong terminals, it can zap your entire computer system. Also, a short in the solenoid or starter has the potential to hurt it.
If the rugged plastic housing receives a great deal of vibration, it can create hairline cracks that allow water to seep inside. All it takes is a drop of liquid in the wrong spot to wipe out the electronics. This isn’t typically a common problem, but if you’ve been hitting a lot of potholes or off-roading on very rough trails, it can cause cracks. A broken motor mount is also noted as potentially damaging to the ECM.
However, before you replace the unit, you should double-check the sensor network, since the wiring and individual sensors are considerably more likely to be damaged than the electronic control module. Even if the ECM is having issues, you may not have to replace it.
The ECM Codes
When your automobile isn’t running well, the ECM allows mechanics to plug their diagnostic machine directly into the module. This begins a self-diagnostic procedure inside the unit, and if the problem is in the powertrain or electronic control, the ECM will respond with a five-digit code.
The codes are of three general types:
- Current errors indicate an ongoing problem that’s present during testing.
- Recent errors only show up when the problem isn’t present at the time of testing but were active during the previous power cycle.
- Historic errors are saved to memory inside the unit.
Examples of some error codes include
- Rear O2 sensor has improper air-fuel ratio
- Incorrect battery voltage
- Incorrect coil voltage
- Bank angle sensor error
That’s a small sample of the dozens of possible results. With the code and a competent mechanic, the problem can be immediately identified and remedied – a major savings in time and money.
The Symptoms of a Faulty ECM
Most of the signs of a failing ECM can also be attributed to other causes, so without an error code, it becomes a process of elimination. If your vehicle starts running poorly – especially if it happened suddenly – that’s a good sign that the ECM or one of its sensors has broken. A stalling or misfiring engine is also common for an electronic control module failure.
The most notorious sign that the ECM has failed is the check engine light on the dashboard. While this can be a sign of a failed oxygen sensor, it’s the single most common symptom of a fault in the electronic control system. It’s also a frequent cause of a failed emissions test; if no other cause is located, the ECM should be suspect. A significant decrease in gasoline mileage could be caused by the ECM having an electronic fault as well. Basically, without a fully functional EMS, your vehicle will run very poorly – if at all.
Fortunately, not all faulty ECMs need replacement. Once a qualified mechanic has found the error code, the underlying problem can be tracked down and fixed. If fixing the cause of the ECM failure doesn’t solve the engine issues, then the unit will probably have to be replaced.