DI-4
-
DIAGNOSTICS
ENGINE
158
Author:
Date:
2001 SIENNA (RM787U)
The diagnosis system operates in normal mode
during normal vehicle use. It also has a check mode
for technicians to simulate malfunction symptoms
and troubleshoot. Most DTC use 2 trip detection
logic* to prevent erroneous detection, and ensure
thorough malfunction detection. By switching the
ECM to check mode when troubleshooting, the
technician can cause the MIL to light up for a mal-
function that is only detected once or momentarily
(TOYOTA hand- held tester only) (See page
*2 trip detection logic:
When a malfunction is first detected, the malfunc-
tion is temporarily stored in the ECM memory (1st
trip).
If the same malfunction is detected again during the second
drive test, this second detection causes the MIL to light up. (2nd
trip) (However, the IG switch must be turned OFF between the
1st trip and the 2nd trip.).
Freeze frame data:
Freeze frame data records the engine condition
when a misfire (DTCs P0300 - P0306) or fuel trim
malfunction (DTCs P0171, P0172, P0174, P0175)
or other malfunction (first malfunction only), is de-
tected.
Because freeze frame data records the engine
conditions (fuel system, calculated load, engine
coolant temperature, fuel trim, engine speed, ve-
hicle speed, etc.) when the malfunction is detected,
when troubleshooting it is useful for determining
whether the vehicle was running or stopped, the en-
gine warmed up or not, the air-fuel ratio lean or rich,
etc. at the time of the malfunction.
Priorities for troubleshooting:
If troubleshooting priorities for multiple DTC are given in the ap-
plicable DTC chart, these should be followed.
If no instructions are given troubleshoot DTC according to the
following priorities.
(1)
DTC other than fuel trim malfunction (DTCs P0171,
P0172, P0174, P0175) and misfire (DTCs P0300
-P0306).
(2)
Fuel trim malfunction (DTCs P0171, P0172, P0174,
P0175).
(3)
Misfire (DTCs P0300 - P0306).
