DDEC I

Specific information on the Detroit Diesel Electronic Control (DDEC) Generation I

DDEC I Schematics

DDEC I Schematic Diagram

This system utilizes an engine mounted EDU and a cab mounted ECM, which has a replaceable Programmable Read-Only Memory (PROM). The EDU functions as the high current switching unit for the actuation of the injector solenoids and is fuel-cooled. ‪

The DDEC I ECM is a microprocessor. It is the control center of the DDEC I system.

The DDEC I ECM is packaged in a die-cast aluminum housing with sealed connectors.

The DDEC I system consists of the following: ‪

• The DDEC I ECM
• A replaceable PROM
• Connections to various engine sensors, operational displays, power and fuel injectors

DDEC I controls the timing and amount of fuel injected into each cylinder. The system also monitors several engine functions using various sensors that send electrical signals to the main Electronic Control Module (ECM). The ECM uses this information to send a command pulse to the Electronic Distributor Unit (EDU). The EDU functions as the high current switching unit for actuation of the Electronic Unit Injector (EUI) solenoids. The ECM also has the ability to limit or shut down the engine completely (depending on option selection) in the case of damaging engine conditions, such as low oil pressure, low coolant level, or high oil temperature.

Owner Notes

Throttle Position Sensor (BB35 drawing coordinates)

• Wire 416A to L1 (AMP CONNECTOR)
• Wire 416 to ECM Module (in rear closet road side)
• Wire 417 to ECM Module (in rear closet road side)
• Wire 452B to High Idle Resistors (K5 drawing coordinates)

JIA ECM Module Connector

• Wire 416 to TPS
• Wire 417 to TPS
• Wire 452 goes to High Idle Resistors (K5 drawing coordinates)

ECU Relay Oil Pressure Switch

• Wire 265 to ECU DIODES
• Wire 258A to ECU RELAY terminal 87

HIGH IDLE RESISTORS (K5 drawing coordinates)

• Wire 452 to connector J1A ECM MODULE
• Wire 452A to EDU (Electronic Distribution Unit)
• Wire 452B to THROTTLE POSITION SENSOR (BB35 drawing coordinates)

ECU DIODES

• Wire 255 Red to K18 (dwg coord) CHECK TRANSMISSION RELAY
• Wire 259 Yellow to R18 (dwg coord) ECU RELAY
• Wire 266 Gray to (B25 dwg coord) 20A breaker

It appears the ECM used in the DDEC I used Motorola components and some OTS (Off The Shelf) hardware used in late 80s GM vehicles.

Oil & Pressure Sensor Locations

Oil Temperature and Pressure Sensor	Oil Pressure Sensor	Turbo Boost Sensor
Oil gauge temperature sensor on my coach is on top of the oil filter and the Dash Oil Pressure Gauge sender and low oil pressure sensor is mounted to the lower rear frame curb side adjacent to the muffler. The Kysor LOW OIL PRESSURE SENSOR 3 lb. is associated with the Check Transmission Light as well as a secondary power source for the ECU Relay. There is a 24" oil hose connected to the rear oil gallery above the starter which feeds the sensors.	The above oil pressure sensor is for the ECM Computer only. Road side near transmission

Troubleshooting

DDEC I Trouble Codes

Code	Description
12	Power Take-Off Speed Adjust (PTOSA) - System on for more than 2 seconds with more than a full PTOSA speed request.
13	Coolant Level Low - System running for 2 seconds with a low sensor output.
14	Low Oil Temperature - Engine running for 8 minutes with a very cold (less than 0° C) oil temperature indication.
15	High Oil Temperature - Engine running for 2 seconds with a very hot (greater than 170° C) oil temperature indication.
16	Coolant Level High- System running for 2 seconds with a high sensor output.
21	High Throttle Position - System running for 2 seconds with too high a throttle position indicated.
22	Low Throttle Position - System running for 2 seconds with too low a throttle position indicated.
25	No Codes - No fault codes have been detected by DDEC since the last time codes were cleared.
26	Power Control Switch - Indicates that the power control switch has been used. This switch, when thrown, turns on both the "Stop Engine" and "Check Engine" lights. In addition, the engine will begin to "power down" (and eventually shut down) if the engine protection system is equipped with the optional shut-down feature.
311 to 318	Response Time Too Long - The response time of the injector was longer than the maximum limit or the injector never responded at all. Oil temperature must be greater than 20 degrees C and battery voltage must be between 11 and 16 volts to log this code.
321 to 328	Response Time Too Short - The response time of the injector was shorter than the minimum limit. Oil temperature must be greater than 20 degrees C and battery voltage must be between 11 and 16 volts to log this code.
33	High Turbo Boost Pressure - Engine idling (at less than 1000 RPM} for 2 seconds with a very high (greater than 197 KPa) turbo boost indication. Also, pulsewidth must be less than 10 degrees to log this code.
34	Low Turbo Boost Pressure - Engine running for 2 seconds (at greater than 300 RPM) with a very low {less than 19 KPa) turbo boost indication.
35	High Oil Pressure - Engine running for 2 seconds with a very high (greater than 422 KPa} oil pressure indication. Must also have greater than 50 degrees C oil temperature and be at less than 1300 RPM to log this code.
36	Low Oil Pressure - Engine running for 2 seconds with a very low (less than O KPa) oil pressure indication. Must also have greater than 50 degrees oil temperature and greater than 300 RPM to log this code.
41	Timing Reference Sensor Pulses Fault - The number of TRS pulses received per revolution was incorrect or completely missing. One pulse per cylinder per revolution 1s required.
42	Synchronous Pulses Fault - Did not receive an SRS pulse on every firing of the #1 cylinder.
43	Low Coolant - System running with low coolant for 7 seconds. This fault will cause both the "Stop Engine" and "Check Engine" light to turn on, and will power down (and eventually shut down} the engine if the engine protection system is equipped with the shutdown feature.
44	Oil Over Temperature - Oil temperature over a maximum limit (about 128 degrees C} for 7 seconds. Both the "Stop Engine" and "Check Engine" lights will turn on and will power down (and eventually shutdown) the engine if the engine protection system is equipped with the shutdown feature. (NOTE: If the oil temperature 1s between 121 and 128 degrees C, no code will be logged, but the "Check Engine" light will come on after 2 seconds and power down the engine if equipped with the power down feature (but won' t power it down as severely as with the 128 degrees C limit.)
45	Low Oil Pressure - Engine running wf th the 011 pressure less than the limit (different limits at different RPM's) for 7 seconds. This fault will cause both the "Stop Engine'' and "Check Engine" light to turn on, and will power down (and eventually shutdown) the engine if the engine protection system is equipped with the shutdown feature.