1992/03/23 Caterpillar

3406B ( 8TC3565-Up, 5YG, 2EK ) PEEC, 3406B ( 4CK1-845 ) PEEC III, 3406C ( 4CK846-Up ) PEEC III Truck Engines

This information is applicable to 3406B (8TC3565-Up, 5YG1-Up, 2EK1-Up) PEEC, and 3406B (4CK1-845) PEEC III, 3406C (4CK846-Up) PEEC III Truck Engines and, 3406B (8TC) PEEC Truck Engines that have had a Personality Module with serial number 20,000 or greater installed.

Symptoms

Electrical noise (voltage spikes) in the truck electrical system has been found to cause malfunctions in the 3406B PEEC Truck Engines equipped with permanent fault logging. Typical sources of the electrical noise are relays or solenoids (such as those controlling engine cooling fans, compression/exhaust brakes, and air conditioner compressors) switching on or off. Symptoms caused by the electrical noise are:

* Engine speed "burps" or

* ECM restarts or

* erroneously logged fault codes

These symptoms occur ONLY on those PEEC truck engines equipped with permanent fault logging. These include 3406B Truck Engines 8TC3565-Up, 5YG1-Up, 2EK1-Up, 4CK1-845, and 3406C 4CK846-Up, or any 8TC PEEC engine that has been retrofitted with a personality module having a serial number above 20,000. No component failures have been confirmed to be caused by this noise, only the above malfunctions.

Symptoms associated with electronic control module (ECM) restarts are similar to those associated with intermittent electrical power. Typically, the diagnostic lamp comes on for a few seconds and no faults are logged. If vehicle speed is above 30 mph, the engine resumes normal power after a second or two. If vehicle speed is less than 30 mph, PEEC goes through its cold mode checks again. During the cold mode checks, engine speed is limited to 1700 rpm, timing advance is inhibited and power is severely limited.

Any fault can be logged erroneously as a result of this electrical noise, including Fault Code 48 (Excessive Engine Power), the code used to log the occurrence of tampering.

One indication of erroneous logging is any logged occurrence of Fault Codes 00, 31, 33, 34, 35, 53, 56, or 57. None of which are intentionally logged. Another indication is numerous, unrelated faults logged at the same time on the PEEC diagnostic clock.

Solution

As the field population of trucks age, checking and cleaning of both the power and ground circuits associated with the PEEC system should be part of the troubleshooting process. This includes running wires from Pin B on the Road Speed Buffer and Throttle Position Sensor to the same ground point as the ECM.

Connecting an inexpensive diode across the coil of the relay or solenoid, as shown in Illustration 1, will prevent voltage spikes from occurring. The diode should be rated for at least 200 volts at 2 amps. An applicable 5N4988 Diode is available from Caterpillar. Freightliner part number A06-17895-003 is also applicable. Similar diodes are available at most electronic supply stores.

Illustration 1. Typical schematic of diode (1) installed on relay (2) and solenoid (3).

Illustration 2. Electrical (1) and physical (4) representation of a diode. Electrical current flows in the direction of the arrows.

If Fault Code 48 is logged, DO NOT immediately assume that tampering has occurred. It could have been logged erroneously. If tampering has actually occurred, one or more of the following signs will also exist:

* Wires to the rack brushless torque motor (BTM) will show physical signs of tampering. The insulation will have been stripped or show signs of having been probed.

* Fault Code 48 will certainly be logged numerous times since the driver rarely tampers with the system just once.

* Fault Code 43 will generally be logged a few times. Fault Code 43 (Rack Subsystem Fault) means that PEEC has tried unsuccessfully to move the rack toward shutoff because the driver was controlling the rack.

* Fault Code 22 (Rack Position Sensor Fault) will sometimes be logged a few times. This means that the rack was moved far enough that PEEC recognized invalid signal from the rack sensor.