On-Board Diagnostic System

How The On-Board Diagnostics Work

The A-604 transaxle controller monitors critical input and output circuits relating to the control of the transaxle. Some of these circuits are tested continuously, and others are checked only during normal driving conditions.

If the A-604 controller senses a problem in the system, a fault code will be stored in the controller's memory. Each monitored circuit has its own designated fault code. Any stored fault code will remain in memory until erased by the technician or until displaced by more recent codes.


FAULT CODES

Fault codes are two digit numbers that identify which circuit is malfunctioning. In most cases they do not pinpoint specific component as defective. It is important to keep in mind that fault codes can be set for hydraulic and mechanical reasons as well as electrical problems.


Hard Fault Codes

Any fault code that comes back a short period of time after it is erased, is called a hard fault. This means the defect is there every time the controller checks that circuit.


Soft Fault Codes

A majority of intermittent failures and the soft faults that result are caused by wiring or connector problems. Defect that come and go like this are the most difficult to diagnose. Intermittent failures must be looked for under the specific conditions which they are reported to occur.


THE A-604 LIMP-IN MODE

The A-604 controller continuously checks for electrical and internal transaxle problems. When a problem is sensed the controller will store a fault code, and for all but six of these fault codes, cause the transaxle to be in a limp-in mode. While in this mode, electrical power is taken away from the transaxle. When this happens, the only transaxle ranges that will function are:

a. Neutral and Park
b. Reverse
c. Second Gear

No upshifts or downshifts are allowed. The position of the manual valve alone allows the three ranges that are available. Although engine performance is seriously degraded while in this mode, it allows the owner to drive his vehicle in for service.