0279175 JOHNSON SWITCH ASSEMBLY. CHOKE

Electronic Controls
The PEEC controller consists of two main components: the Electronic Control Module (ECM) and the Personality Module. The Electronic Control Module (ECM) is the computer which controls a PEEC engine. The Personality Module is the software which controls how the computer behaves. The two must be used together -neither can do anything by itself.When the key is first turned on, the personality module sends the ECM through some self-checks. Until the self-checks are complete, PEEC limits rpm to 1700 rpm, power to about half of normal, and timing advance to zero. It takes about 8-10 seconds to complete the self-checks, during which time the driver should leave his foot off the throttle pedal. If the throttle is depressed during this time, the self-checks are postponed until his foot remains off the throttle to allow the checks to finish. If electrical power to PEEC is briefly interrupted during operation, PEEC goes back through these self-checks to ensure proper operation of its circuits.Rack Controls
The rack mechanism on a PEEC engine is very similar to a mechanical 3406B engine. The fuel injection pump is nearly identical; the rack is moved by a servo valve which receives oil pressure from the fuel injection pump. However, the PEEC servo spool is moved by a solenoid or (BTM) rather than by a linkage controlled by flyweights and springs.PEEC comes up with a "desired rpm" based on the throttle position, vehicle speed, Customer Specified Parameters, and certain diagnostic codes. The PEEC governor tries to maintain the desired rpm by sensing actual engine rpm using the engine speed sensor, then controlling the rack to achieve the desired rpm. To move the rack, PEEC adjusts the voltage to the rack solenoid (BTM) to increase rack. More voltage results in more rack. PEEC knows how far the rack actually went by reading the rack position sensor. PEEC increases the voltage to the rack solenoid until it senses the rack is in the desired position. PEEC sets certain limits on rack motion. "FRC Rack" is a rack limit based on Fuel-Air Ratio Control, for emissions purposes. It works similar to mechanical engine FARC; when PEEC senses a higher boost pressure (more air into cylinder), it increases the FRC Rack limit, which allows more fuel into the cylinder. "Rated Rack" is a rack limit based on horsepower of the engine. It is similar to the rack stops and torque spring on a mechanical engine. It provides horsepower and torque curves for a specific engine family and rating. All of these limits are programmed by the factory into the personality module.Timing Advance Controls
The timing advance mechanism is the same as the 3406B mechanical engine, except the Timing Solenoid (BTM) controls amount of timing advance instead of flyweights. PEEC adjusts voltage to the timing solenoid to change timing advance. More voltage results in more timing advance. PEEC knows how much advance was achieved by reading the timing position sensor. PEEC simply increases voltage to the timing solenoid until it senses that the timing advance is in the desired position. Desired timing advance is controlled by software in the Personality Module, and is dependent on engine rpm, load, and other operation factors. Because of this, the performance specifications do not call out the amount of advance at a specific rpm. The best indication of timing advance specification is displayed on ECAP status screens as "Des Timing Adv".Programmable Parameters
Certain parameters that affect PEEC engine operation may be changed through electronic service tools. The parameters are stored in the ECM, and are protected from unauthorized changes by passwords.Some parameters affect engine operation in ways some drivers may not expect without adequate training. These may lead to power or performance complaints, even when the engine is performing to specification.As an example, Vehicle Speed Limit (VSL) is programmable to allow the customer to electronically limit vehicle speed. When the programmed limit is reached, PEEC limits rpm so that VSL will not be exceeded. Also, Progressive Shift parameters (such as Low Gear limits and High Gear limits) will cause PEEC to pause at a programmed engine rpm to encourage more fuel-efficient driving practices.The section on "Programming PEEC Parameters" in this manual has more details on specific parameters and how to program them.Passwords
"System Configuration Parameters" are protected by factory passwords. System Parameters are those that affect horsepower family or emissions. Factory passwords are calculated on a computer system available only to Caterpillar dealers. Since factory passwords contain alphabetic characters, only the ECAP may change System Parameters."Customer Specified Parameters" are protected by customer passwords. Customer Parameters are those that affect cruise control, vehicle speed limits, progressive shifting, horsepower rating within a family, and PTO operation. The customer passwords are programmed by the customer. Either the ECAP or DDT may normally change Customer Parameters. However, if a customer uses alphabetic characters in his password, only the ECAP can change Customer Parameters.The section on "Programming PEEC Parameters" in this manual has more details on when passwords are needed and how to obtain them.Self-Diagnostics
PEEC has some ability to diagnose itself. When a problem is detected, a diagnostic code is generated and the diagnostic lamp is turned on. On newer engines (those equipped with personality modules built since April 1989), the code may also be stored in permanent memory in the personality module.Diagnostic Codes that represent current faults are called ACTIVE. They indicate that a problem of some kind currently exists. They should always be serviced first. See the Troubleshooting Diagnostic Codes section in this manual for more details.Diagnostic Codes stored in memory are called LOGGED. The problem may have been temporary or may have been repaired since the time it was LOGGED. Therefore, LOGGED diagnostic codes don't necessarily mean something needs to be repaired. They are meant to be an indicator for when intermittent problems exist. In addition, some logged diagnostic codes record "events", rather than failures. See the section on "Troubleshooting Diagnostic Codes" in this manual for more details.(PEEC) System Component Diagram
For Electrical Schematic, refer to Form No. SENR3486.
Location Of PEEC