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ECM – Electronic Control Modules

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Beginning in the early 1990’s, diesel truck engines were being equipped with electronic engine controls. The electronic engine controls were initially used to control the diesel fuel injection systems that were being installed to meet more stringent federal emission requirements. As the systems became more sophisticated, the engine manufacturers began adding features at the request of the equipment purchasers. These features began as simple trip recorders and evolved into the sophisticated systems that we have today.

The information that can be retrieved from the engines electronic control module (ECM) varies from year to year and the manufacturer of the engine.

The following is a brief overview of what information is available.

Caterpillar began installing electronic engine controls in 1993.

Caterpillar refers to a hard stop as a “quick stop” in their software. The quick stop feature became available in November of 1995.

The quick stop is set at a deceleration rate of 0 mph/sec./sec. at the factory. It can be set by the chassis builder, by the selling dealer, or occasionally, by the end user. The available settings are from 0 to 15 mph/sec. although Caterpillar recommends a setting of 7 mph/sec.

A quick stop event will be recorded in the RAM memory of the ECM if the threshold setting is reached. An internal battery backs up the RAM memory and the stored information will remain in the memory for seven to ten years. It will record the engine hours, engine rpm, throttle position, clutch switch position, brake switch position, cruise control status, and vehicle speed for 44 seconds before the event and 15 seconds after the event in one-second intervals. The ECM stores one quick stop event. Any subsequent quick stop events will replace the oldest one that is stored. The ECM also logs a diagnostic code event at the time the quick stop event is recorded. This diagnostic code event records oil pressure and temperature, coolant pressure and temperature and any faults in the electronic systems such as fuel injector faults, open circuits, etc.

Caterpillar calls their trip computer the “Cat Driver Information Display.” This unit is a sophisticated device that monitors such items as average fuel mileage, instant fuel mileage, trip time, trip distance and other information that can assist in accident reconstruction. This device can be programmed to enable the driver to reset all the trip information with the exception of the quick stop data.

Cummins Engine Company ECM
The Cummins electronic fuel injected highway engines have had the option of a “Road Relay” dash mounted display since 1993. This display is a sophisticated trip computer that can also advise the driver of engine related problems.

If the truck is equipped with this Road Relay option, the hard stop information is available for downloading.

Cummins is on their fourth reiteration of this dash mounted display device and it is called the Road Relay 4.

The earlier Road Relays could only show the number of panic stops in the last trip. The Road Relay 4 also shows 75 seconds of data that includes mph, engine rpm and the brake and clutch activity for the last three hard stops. It will also show the number of times the truck was coasting out of gear.

The hard stop feature is enabled from the factory and is set at a deceleration rate of 9 mph/sec. It is adjustable from 0 to 99 mph/sec. for the Road Relay 3 and from 0 to 30 mph/sec. for the Road Relay 4.

Detroit Diesel Corporation

Detroit Diesel calls their electronic engine control system Detroit Diesel Electronic Controls (DDEC). Beginning with DDEC in 1992, the hard stop feature became available as a customer definable feature. The default setting from the factory is in the off position.

When the engine is equipped with DDEC II or III, a hard stop event is recorded in the memory and remains there until cleared by a Pro Link or Detroit Diesel sourced software.

Beginning with DDEC IV in January 1998, the hard stop feature is enabled from the factory and set at a deceleration rate of 7 mph/sec.

With DDEC IV, the memory for a hard stop was expanded to include information for 15 seconds after the event and 1 minute before the event. The information recorded is road speed, engine rpm, brake application, clutch position, engine load, cruise control operation, trip date, trip distance, fuel used, fuel economy, average engine load, average vehicle speed, trip time, fuel consumption, idle time, idle percentage, fuel consumed while idling, odometer reading, incident time, incident odometer reading and vehicle ID.

In addition to the above incident information, the DDEC system will also generate 36 pages of reports that include trip activity, vehicle speed/RPM, engine load/RPM, vehicle speed/RPM and diagnostic records. If the unit is equipped with a Pro Driver (a dash mounted display), five hard stop events will be stored within the Pro Driver unit.

The information is stored in what Mack calls the DataMax Database. The DataMax Database is stored in the ECM (electronic control module). The ECM is referred to by Mack as the V-Mac Engine Control Unit. Mack uses two ECMs in their units. One ECM is mounted on the engine and another is mounted on the chassis. The following information is recorded in the database on DataMax 3 units built in the last quarter of 1998 and later:

Trip time, fuel, distance, moving time, fuel, distance, cruise time, fuel, distance, faults, fault count, fault time, hard braking occurrences, maximum trip MPH and RPM, severe over RPM occurrences and values.

The following information is under the heading of Histograms in the ECM (electronic control module):

MPH vs. RPM vs. Time

MPH vs. RPM vs. Fuel

MPH vs. Miles vs. Distance

The following information is under the heading of Incident Log in the ECM:

Vehicle MPH

Engine RPM

Pedal positions

Dash switch positions

The following information is under the heading of InfoMax Reports in the ECM:

Driver summary report

Driver event/over speed report


Incident report

Vehicle fault log/summary

The incident threshold is set at a deceleration rate of 10 mph/sec, although the ECM will log an incident at a lower deceleration rate during certain instances.

Freightliner Trucks
Beginning in January 2000, all Century Class S/T trucks are equipped with a data-logging unit (DLU) that will record a hard stop upon deployment of the driver’s side air bag or a near deployment.

The DLU is cab mounted and interfaces with the engine ECM and if equipped, the transmission ECM.

The DLU will record the road speed, brake status, accelerator position, engine retarder status, cruise control status, cruise control set speed, ambient outdoor temperature, odometer mileage, current date and time. The DLU will record the information for 4.25 minutes before and one minute after the air bag deployment. The DLU can store up to 50 separate events in its permanent memory.

Eaton Vorad
The Vorad system is a sophisticated radar that can be fitted on any truck. Its primary purpose is to warn the driver of objects or vehicles getting too close. The system has warning lights that warn the driver as the objects are getting within 3 seconds, 2 seconds, 1 second and l/2 second away.

The standard Vorad system comes equipped with one forward facing radar sensor. The system can also be equipped with a side sensor that is mounted on the right side of the truck that can detect the presence of an object to the side of the truck. The system records the distance, speed and angle of up to 20 vehicles in front of the truck. It also records the truck speed and its turn rate as well as other parameters.

Qualcom is the leading manufacturer of satellite tracking equipment as it is used in the trucking industry today. The Qualcom system gives position data of the truck and up to eighty-eight other types of data, depending on the options that are selected by the end user. The available data can include position data, engine rpm, speed, brake applications, average speed, trip distance and many others. Qualcom stores up to fourteen days of position data and up to ninety days of message data at their facility. The Qualcom unit obtains most of the vehicle data through the engine ECM.

Antilock Braking Systems (ABS)
ABS systems as they relate to heavy-duty trucks have been in use since the 1980’s in the USA. Beginning March 1, 1997, all air brake equipped tractors built after this date and all air brake equipped trucks, trailers and buses manufactured after March 1, 1998 must be equipped with ABS as required by federal law.

The ABS systems that are installed on air brake equipped vehicles are electronically controlled and utilize an electronic control module (ECM) to operate the system that is typically linked to the engine ECM.  This ECM also stores fault codes that can later be retrieved for diagnosis of an inoperative or malfunctioning system.

The typical air brake ABS system utilizes wheel speed sensors on some or all of the wheels and transmits the information to the ECM. The ECM compares the wheel speed information from the other wheel speed sensors and then determines if one or more of the wheels are decelerating at a rate that will cause the wheel(s) to lock up. If the ECM determines that the wheel(s) is (are) approaching lock up, it will close the modulator valve at that wheel(s) and prohibit the passage of any additional air to the brake chamber. When the ECM senses that the wheel(s) speed in is in line with the others, it will open the modulator valve and let additional air pressure enter the brake chamber and the process begins again. This process occurs up to six times per second.  After an accident occurs, the ABS ECM can be interrogated by brand specific software to determine if the ABS system was operating properly at the time of the accident.

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