ECM failures -- Fact or fiction:

The fact is, the models of ECMs and TCUs utilize certain components that after a certain number of hours or mileage, begin a systematic breakdown. Most units are repairable unless there is damage to a part that is not made available to us.  Presently, their are specific components that are damaged occasionally that we can not purchase.  We are the first company to specialize in this field and we have the best technicians in the business.  The hardest component to acquire is the processor chips.  The processor chips are imbedded chips or IC chips that contain vital information which is copy written and is likely not to be able to access.  In most cases when the IC chip or chips are damaged, they will experience a heat to the imbedded chip which will damage the chip and often a heated IC will have a variance on the smooth surface of the chip from the heat.  The variance may be in the form of a bubble or rise or in some cases a hole or crack is blown though.  In these cases, we will likely recommend to replace the ECM. When this occurs, you will be informed of the change in the price quote and upon permission, we will attempt to acquire a replacment ECM for the additional cost.  The warranty will not be affected.

Between 1985-1999, engineers manufactured Electronic Control Modules ECMs with great design and precision.  One problem has been revealed over the years: some of the components that were used have shown a tendency to fail, especially by heat.  The heat from the normal operation of the current in the unit and the heat from the environment the ECM unit is stored in. Some models are stored in the cab which can reach temperatures of up to 140f.  Some models are stored in the engine compartment which is the worse possible environment for a computer processor.  The engine compartment is exposed to the elements of the environment outside and the engines operating environment.   Normal operations can adversely affect the ECM unit over time as well.  Components such as the ECS, the ISC, TPS, engine sensor, alternator or failing batteries can adversely affect the unit.  Reversing polarity when jump starting vehicle can damage the ECM.

The most prominent candidates for failure are those installed during the 1985 through 1999 model years with 60,000 or more miles.  It is also true that hotter climates contribute to increased failure probability.  In other words, the Southern States: Texas, Florida, Georgia, and even Hawaii, have a higher number of failures than the Northern States.

The supply of ECMs new and used has been greatly reduced due to the growing competitiveness of this industry. Keep in mind most of these quote-unquote "Rebuilders" are more than likely people that have seen the trend in ECM failures and are trying to capitalize. I'm all for free enterprise -- after all, this is America and may God Bless her (and all of us for that matter) but don't let yourself be fooled by the new kids on the block. Nor should you be mislead by the low prices of some of these folks. If it sounds to good to be true and too cheap to be quality, it probably is. You know you can't wager your safety or that of your family or customers to the opportunity of a "great deal".  Check references! A lot of these guys offering warranty's and advertising themselves as rebuilders have not been in business long enough to match the warranty they are offering!

We are proud members of the Better Business Bureau and the Automotive Parts Rebuilders Association.  We HIGHLY RECOMMEND you check with the BBB before you give out your hard earned money to someone who may be well behind the learning curve for ECM repair.  It is simple to do and may save you money and time.  If nothing else, ask the prospective supplier or "rebuilder" if they are members of the BBB or if they have ever had any complaints registered with the BBB.  Also be sure they have actual test vehicles to test the repairs.

Also be aware of the used units often sold in salvage yards. Although the automobile salvage and recycling industry is vital to my company and the world even, make sure you understand the difference between a "USED" unit and a "REBUILT" unit or even a "REPAIRED" unit. All these are different classifications.  Many times when you are dealing with a foreign manufactured ECM not in the ECM hot zone, a used unit is a solid safe and money saving alternative.  But it is VERY IMPORTANT to remember any product (1989-1999) will have the same manufactured components that are often the problem with the ECMs failure.  So before you buy a used unit with little or no warranty just to "save a few bucks", factor in the failure probability.

Our knowledgeable staff will help you with better understanding the reason you may be experiencing computer problems or even help prove you don't have a computer problem at all. That's right, Automotive Computer Supply can test Most units in the "Problem Zone" (manufactured years 1989-1996) and tell you if it is the ECM or another possible related or unrelated electrical problem. We would be happy to help you SAVE MONEY!!               


Many OBD-II computers in cars are now equipped with the greatest technology available. At the factory, they must be flashed or programmed to fit the specific requirements of the make and model and application.  You can no longer acquire a used unit and install it into the vehicle, nor can you just repair them.  Once they are removed, they loose their programming in most cases and MUST be reprogrammed to the application as specified by the VIN (vehicle identification) number. OBD-II computers' attributes specific to these models is often the way they are manufactured (jell filled-designed to keep moisture and heat from adversely affecting the unit) and the way they are mounted (inside engine compartment often to the engine).  This design was intended to better fit the technology.  The problem is they are exposed to the elements the engine is exposed to and are still damaged from movement and from internal heat. 




Many people are surprised to find out they have a computer in their car!  Many newer models may have more than seven independent and cooperative computer controller devices aiding in the performance, comfort and environmental factors.  They are even more astounded when they find out that the cost is anywhere from $650 to $2000 for a new unit from the dealership!  To understand the ECM we can help by a short history of the ECM and implementation of computer controlled electronic systems.   The Federal Government implemented the use of computer controlled ignition and fuel systems for 3 main reasons:

  1. To aid in the safety of the consumer
  2. To better economize the fuel consumption
  3. To reduce the output of EPA regulated byproducts of the ignition controlled internal combustion gas/diesel fueled engines in passenger and commercial vehicles

Often when your computer is failing there is misdiagnosis and people will spend hundreds I've even seen customers who have unfortunately paid over a $1000 on their car on repairs and part replacement before he finally got to us and he found out he needed only an ECM to solve his problem. I have seen people go without their vehicles for months because the mechanic could not find out he had a computer failure.  On the other hand their have been countless others who have paid this amount and more on new computer ECU(s) and the problem does not go away!  The key is proper diagnosis!  My father always said measure twice cut once.  So we are firm believers in getting a second opinion or third if necessary to collaborate repair diagnosis that can be financially crippling.

Most common misdiagnosed parts are battery, distributor, ISC motor, TPS switch, injectors & intake cam sensor, and other sensors or bus system including but not limited to the harnesses.  If the technician does not figure it is the ECM they may sell you parts you may not need.

When diagnosing an efi or electronic fuel injection system vehicle, here are the "inside" industry approach procedures to engine computer, or otherwise diagnosing a malfunctioning vehicle.  These systems all require the same basic elements, and by checking all individually, you may be able to rule out and systematically diagnose your problem and save hundreds of dollars. 

First assess your symptoms. 

Is your car starting and running, but stalls or seems to not idle right.

  • If so, is the check engine light illuminated  MIL or (malfunction indicator lamp) on intermittent or all the time?

  • If so, what are the MIL DTC diagnosis codes? Try pulling ECM and looking and smelling for burns.  Have your ECM tested to be sure it is functioning properly.  If the ECM is bad, have it repaired or replaced with known remand or new unit. see www.ECMtogo.com

  • If ECM is OK, then follow the error codes it gives, and check the appropriate malfunction (i.e.: check engine light coded you had bad oxygen sensor, try unplugging it and restarting car to see if any change in running or the MIL.  If no change, try putting a known good used unit in, or buy new unit if in your budget.)

  • Have ECM scanned in car by authorized tech with proper scan tools specific to application (only after installing or verifying you have a good ECM).  Most manufactures have specific tools to there equipment even though there are many scan tools that can do basic diagnosis.  This scan should show what elements are giving you the problems.  There are some ways to check error codes without scan tool.  Refer to manual for key to specific application.

  • This insider tip is for Mitsubishi & Chrysler Vehicles and is quite helpful for diagnosing or testing your ECM.  You need a analog volt/ohmmeter, put the  testers on pin 1 and pin 12 (top right & bottom left pin) of diagnosis ECM scan cable harness.  This harness is inside the cab area, usually in drivers side upper left of drivers kick panel.  The sweeping motion left to right means ECM is OK.  Sweep right to left means reverse testers to pin 12 and pin 1.  A movement to the right without bounce or return means bad ECM.

  • Many models also have ways to check the MIL codes an indicator light on the dash or ecm or will illuminate the check engine light in series indicating the first digit then the second digit will follow and the indicators will repeat.

Your car Is not starting?  As we started earlier, all efi engines need the basic elements to run: 

  1. battery power send voltage to starter to crank over the engine, and voltage references to and from ECM computer and supply power to relative components for vehicle operation

  2. starter/solenoid

  3. injector pulse- voltage reference from ecm to injector(s)

  4. fuel (ecm sends voltage reference often via mpi relay to fuel pump)

  5. spark to spark plugs to ignite the fuel/oxygen mixture for usable power

Knowing this you can then systematically check these separately.....

  • Power- battery/alternator system:

  1. If you have lights, you may be OK for cranking. But if she's sat up for a while, you may want to have a battery charger or power/booster charger available and attached to your battery with a good grounded connection.

  2. If no lights check battery voltage with multi-meter.  If less than 12 volts check alternator. 

  3. If alternator bad replace, else replace battery.

  4. If you hear clicking and have power, check starter/solenoid. (Try tapping on the starter with a wrench a couple times.  This sometime can be a temporary fix to free up the locked solenoid which often locks and won't engage.  Replace Starter or solenoid with known good remand or OEM model.

  • Injector pulse:

   put a node light or meter on injector #1 to see that the ECM is sending injector pulse.  If not pull ECM and look and smell for burns.

  • spark to plugs

   check for spark at plugs, check the following if applies to your vehicle:  distributor (coil, igniter, crank angle sensor, cam sensor), relay, ecu

  • fuel/fuel pump reference

  1. check voltage reference from ECM or from mpi relay to fuel pump.  You can often hear it kick in. You can also see the flow from pump to ensure it is solid.  Be sure to do this in controlled environment!  IF fuel pressure is normal, it will shoot across the room! Have a volatile fuel receptacle ready like a larger glass jar or gas can

  2. If you have no voltage reference to fuel pump, check relay.  If relay OK, check ECM for burns or smells.  Test ECM.

  3. If reference to fuel pump but no fuel pressure, check fuel pump.


Engine Ignition and fuel management system components:

We will now list components of your vehicle ignition and fuel management system which directly or indirectly affect your computer's processing ability.  If the component is faulty it can hinder performance and lead to misdiagnosis of bad computer unit by giving bad vital info to the ECU computer unit.   Some of these components can possibly damage the computer unit.  

Conversely, when your computer unit is damaged, it cannot process the info to affectively manage the vehicle's system for optimum performance.  This can actually adversely affect performance and lead to harder diagnosis and more opportunities for misdiagnosis.

            crankshaft or camshaft position sensor 

Monitors engine rotation and tells the computer exactly when to trigger the fuel injectors or the ignition spark.

       mass air flow sensor/MAF

Measures the amount of air drawn through the engine's air intake, so the computer can compensate for altitude and temperature.

   oxygen sensor/EGO sensor

Measures the percentage of oxygen in the exhaust, and tells the computer whether the fuel/air mixture is too lean or too rich.

     MAP sensor/BAP sensor

Reads changes in barometric (air) pressure. The ECM uses this information to adjust timing advance and air/fuel ratio.

   ignition coil

Converts the car battery's 12 volts to the thousands of volts needed to fire the spark plugs.

    idle speed control motor actuator ISC

Adjusts idle speed as dictated by the ECM, to prevent idle fluctuations and keep emissions low.

    EGR valve position sensor

Detects the opening of the EGR valve, so the ECM can make adjustments to
optimize performance and emission control.

  throttle position sensor TPS

Monitors the position of the accelerator control and the throttle linkage.  The ECM monitors this info to make accurate air/fuel mixture adjustments.

   coolant temperature sensor CTS 

Measures the temperature of the coolant in the cooling system, so the ECM can make adjustments based on the engine's  operating temperature. Also can control the dashboard warning light.

     voltage regulator

Controls the voltage supplied to the car's electrical system, preventing overcharge, undercharge and damage to electrical computers.

      fuel injector

Injects fuel into the intake manifold. The ECM tells the injector exactly when to inject, and how much to inject, to produce the needed amount of power based on all the sensor info read by the computer unit.

  electronic control module/unit ECM/ECU/PCM

Controls ignition system's spark and timing, fuel system's fuel delivery and emission controls. Continuously receives signals from sensors and input devices on or near the engine; sends control signals to valves, controllers and other output devices. Stores "trouble codes" and warns driver when service is needed via check engine light or malfunction indicator light (MIL).



email us here       Toll Free call 800.817.7531 sales direct & South Florida call  954.514.7751

Servicing hundreds of Dealerships and Repair Shops & helping people via the World Wide Web since 1997

copyright ©1997-2013 ECM TO-GO Auto Computer Pro, LLC & John Brian South all rights reserved