Notes Regarding On/Off Ratio Check & Impulse Readout

Notes Regarding on-off ratio check using on-off ratio tester

The operation of the on-off ratio control can be tested by checking the on-off ratio. In addition any malfunctions that exist momentarily can be recognized. The tests distinguish between malfunctions that occur with the ignition ON or with the engine at idle.

The on-off ratio can be checked using the on-off ratio tester or engine analyzer. An on-off ratio of 50% indicates that all input signals are OK, but on-off ratio control is not functioning. A varying on-off ratio indicates that the on-off ratio control is functioning correctly. On-off ratios from 10% to 95% are each assigned a specific malfunction (See Computers and Control Systems, Testing and Inspection). After testing the on-off ratio, a diagnostic trouble code (DTC) readout using the impulse counter scan tool must always be performed.


Notes Regarding DTC readout using Impulse counter scan tool

When diagnosing engine running complaints, or when the CHECK-ENGINE lamp is illuminated, the DTC memory should be read out and the DTC's noted before any repairs are attempted. This will ensure that the technician can differentiate between actual malfunctions and "simulated malfunctions," since testing done on a running engine will cause malfunctions to be stored that were caused by a simulation or a disconnected circuit.

When testing is completed, the DTC memory of the LH-SFI control module, base module, DI control module and the EA/CC/ISC control module or CC/ISC control module must be cleared.

1. Connect impulse counter scan tool according to diagram. Connection Diagram - Impulse Counter Scan Tool
The LED U-Batt" should come on. If not, check the following:
a) Voltage supply.
b) Impulse counter scan tool fuse.

2. DTC memory readout:
a) Ignition: ON.
b) Push start button for 2-4 seconds.
c) Read and record DTC readout.
d) Push start button again.
e) Read and record DTC readout.

Repeats steps d) and e) until the first DTC readout reappears.

3. Clearing DTC memory:

NOTE: The clearing process must occur within 20 seconds after the DTC readout.

a) Ignition: ON
b) Push start button 2-4 seconds (Impulse display appears).
c) After a waiting period of 3 seconds, push the start button for 6-8 seconds which will erase the previously displayed DTC.
d) Erase each DTC separately.
e) Turn OFF ignition for at least 30 seconds.