Engine Control Computers

Today's automotive technology is incredibly powerful. Do you realize a simple greeting card that plays music has more computer power than anything that existed in the entire world before 1950? The average consumer wears more computing power on their wrists than anything that existed in the entire world before 1961. Today's automobile has more computer brain technology than the first Lunar space module. How do we keep up with this ever-changing technology? TRAINING! Almost everybody has at least one VCR at home. Here's a quick test to see if you are capable of performing automotive electronic repairs. Look at the clock on your VCR. If it flashes 12:00 all day long, you may have trouble performing automotive electronic repairs. But if you can set the time, program the VCR to tape your favorite program and know how to use a remote control, then you can easily fix and repair today's Smart cars.

Let’s look at automotive computers on a simplified level. An ECM (engine control computer) is merely a glorified calculator. The ECM sees numbers from sensors, also known as inputs. It then calculates the information and sends numbers to solenoids, also known as outputs. This process is similar to the human body. When you touch a hot object, nerves (sensors) in your finger send a signal through the nerve cells in your body and into your brain. The brain, like the ECM, makes decisions based on inputs from the nervous system and determines what actions should be taken to correct the situation. The brain then sends a signal to the hand and arm muscles (output) and stimulates the body to move away from the hot object in a relatively short amount of time. It’s a simple process, unless of course, there is a problem.

The ECM monitors and regulates engine functions, emission gasses, as well as optimizes engine performance and fuel consumption. Systems controlled by the ECM include fuel delivery, EGR (exhaust gas re-circulation), evaporative system, air management, TCC (torque converter clutch) and spark timing. The ECM is constantly updated with data (voltage signals) from the sensors (input) about engine operation. Sensors are variable resistors that modify a voltage to or from the ECM. Data is analyzed by the ECM and decision commands (usually ground signals) are sent to control devices (output) based upon inputs from the sensors and ECM preprogrammed memory. There are 3 types of memory used in ECMs. They are ROM, RAM, and PROM. Read only memory (ROM) is a preprogrammed section of memory that can only be read by the ECM. If the battery power is lost, ROM memory is not lost but is retained. Random access memory (RAM) contains information that is moved into and out of the RAM and is constantly updated. Sensor information, diagnostic codes, and calculation results are stored in the RAM. The loss of battery voltage will result in lost data. Programmable read only memory (PROM) is a factory programmed set of instructions containing the calibration data for the particular vehicle’s engine, transmission, body and axle ratio. This memory may or may not be removable depending upon the vehicle manufacturer. If this memory chip (PROM) is removable (GM), it must be transferred to the replacement unit. If the memory is non-removable, the whole ECM must be replaced.

When feedback information affecting the system is out of parameters, the ECM will illuminate the check engine light and a “trouble code” will be stored in the memory. Retrieval of the code(s) will identify the problem circuit or area to be tested. This allows the technician to concentrate on specific circuits affected and perform repairs accordingly. Function tests are then performed to assure the repair is correct and the system is functioning properly.

ECMs rarely fail by themselves. Most ECM failures occur due to overloaded circuits caused by shorted solenoids and/or relays (outputs) that do not meet specified OHMS resistance. All ECM controlled components MUST be checked for proper resistance before the replacement unit is installed or premature failure will result. Bad ground circuits and improper voltages can also lead to erratic operation or damage to the ECM. Voltage supplies should be checked and verified. A good way to test grounds is through a voltage drop test. To perform a voltage drop test, switch the DVOM (digital volt, ohmmeter) to the low volts or millivolt setting and put the positive lead of the meter to the negative terminal of the battery, and the other lead to the ground circuit at the ECM. The voltage reading should be less than .5 volts. Check with the system under a load while wiggling the wires. Voltage over .5 needs to be repaired.

Defects in original equipment ECMs are identified to improve ECM durability. Here are some examples of CARDONE ECM upgrades: installation of heavier injector drivers, circuit protected quad drivers, upgraded power supply diode for the ignition circuit (Chrysler), re-flow of solder joints and revised conformal coating process (GM). However, even with improvements to the product, the majority of ECMs returned to CARDONE as warranties actually test good, or are customer induced failures (shorted solenoids / relays).

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