1996 TOYOTA TERCEL Service Repair Manual

A15708
- DIAGNOSTICSENGINE
DI-67
1996 TERCEL (RM440U)
TOYOTA hand-held tester:
1 Check connection of vacuum hose, EGR hose (See page EC-2).
NG Repair or replace.
OK
2 Check VSV for EGR.
PREPARATION:
Select the ACTIVE TEST mode on the TOYOTA hand-held tes-
ter.
CHECK:
Check operation of VSV, when it is operated by the TOYOTA
hand-held tester.
OK:
EGR system is OFF:
Air from pipe E is flowing out through the air filter.
EGR system is ON:
Air from pipe E is flowing out through pipe F.
OK Go to step 4.
NG
3 Check operation of VSV for EGR (See page EC-7).
NG Replace VSV for EGR.
OK
Check for open and short in harness and con-
nector between J/B No.2 and ECM
(See page IN-26).

DI-68
- DIAGNOSTICSENGINE
1996 TERCEL (RM440U)
4 Check EGR vacuum modulator (See page EC-7).
NG Repair or replace.
OK
5 Check EGR valve (See page EC-7).
NG Repair or replace.
OK
6 Check manifold absolute pressure sensor (See page DI-23).
NG Repair or replace.
OK
Check and replace ECM (See page IN-26).
OBD II scan tool (excluding TOYOTA hand-held tester):
1 Check connection of vacuum hose, EGR hose (See page EC-2).
NG Repair or replace.
OK

A15709
- DIAGNOSTICSENGINE
DI-69
1996 TERCEL (RM440U)
2 Check VSV for EGR.
PREPARATION:
(a) Turn up the floor mat on the passenger side.
(b) Remove the 2 bolts for ECM.
(c) Disconnect the ºE5º or ºE8º connector of ECM.
(d) Turn the ignition switch ON.
CHECK:
Check VSV function
(1) Connect terminal EGR of the ECM connector and
the body ground (ON).
(2) Disconnect terminal EGR of the ECM connector
and the body ground (OFF).
OK:
(1) VSV is ON:
Air from pipe E is flowing out through pipe F.
(2) VSV is OFF:
Air from pipe E is flowing out through the air filter.
OK Go to step 4.
NG
3 Check operation of VSV for EGR (See page DI-65, step 3).
NG Replace VSV for EGR.
OK
Check for open and short in harness and
connector between J/B No.2 and ECM
(See page IN-26).
4 Check EGR vacuum modulator (See page EC-7).
NG Repair or replace.
OK

DI-70
- DIAGNOSTICSENGINE
1996 TERCEL (RM440U)
5 Check EGR valve (See page EC-7).
NG Repair or replace.
OK
6 Check manifold absolute pressure sensor (See page DI-23).
NG Repair and replace.
OK
Check and replace ECM (See page IN-26).

- DIAGNOSTICSENGINE
DI-71
1996 TERCEL (RM440U)
DTC P0402 Exhaust Gas Recirculation Flow Excessive
Detected
CIRCUIT DESCRIPTION
Refer to DTC P0402 on page DI-65.
DTC No.DTC Detection ConditionTrouble Area
P0402
After the engine is warmed up, conditions (a) and (b) continue
(a) The intake manifold absolute pressure is larger than the
value calculated by the ECM while the EGR system is ON
(b) Misfiring is detected during idling
(2 trip detection logic)
EGR valve stuck open

Vacuum or EGR hose is connected to wrong post

Manifold absolute pressure sensor

ECM
INSPECTION PROCEDURE
HINT:

If DTC P0105 and/or P0106 and P0402 are output simultaneously, perform troubleshooting of DTC
P0105 first.

If DTC P0401 and P0402 are output simultaneously, perform troubleshooting of DTC P0402 first.
1 Check connection of vacuum hose, EGR hose (See page EC-2).
NG Repair or replace.
OK
2 Check EGR valve (See page EC-7).
NG Repair or replace.
OK
3 Check VSV for EGR (See page DI-65).
OK Go to step 5.
NG
DI95Q-01

DI-72
- DIAGNOSTICSENGINE
1996 TERCEL (RM440U)
4 Check operation of the for EGR (See page EC-7).
NG Replace VSV for EGR.
OK
Check for open and short in harness and con-
nector between engine room R/B and ECM
(See page IN-26).
5 Check EGR vacuum modulator (See page EC-7).
NG Repair or replace.
OK
6 Check manifold absolute pressure sensor (See page DI-23).
NG Repair or replace.
OK
Check and replace ECM (See page IN-26).

FI7081
Waveform of Oxygen Sensor
before CatalystNormal CatalystWaveform of Oxygen
Sensor after Catalyst
- DIAGNOSTICSENGINE
DI-73
1996 TERCEL (RM440U)
DTC P0420 Catalyst System Efficiency Below Threshold
CIRCUIT DESCRIPTION
The ECM compares the waveform of the oxygen sensor located before the catalyst with the waveform of
the oxygen sensor located after the catalyst to determine whether or not catalyst performance has deterio-
rated.
Air-fuel ratio feedback compensation keeps the waveform of the oxygen sensor before the catalyst repeat-
edly changing back and forth from rich to lean.
If the catalyst is functioning normally, the waveform of the oxygen sensor after the catalyst switches back
and forth between rich and lean much more slowly than the waveform of the oxygen sensor before the cata-
lyst.
But when both waveforms change at a similar rate, it indicates that catalyst performance has deteriorated.
DTC No.DTC Detection ConditionTrouble Area
P0420
After the engine and the catalyst are warmed up, and while
vehicle is driven within the set vehicle and engine speed
range, the waveforms of the oxygen sensor (bank 1 sensor 1)
and heated oxygen sensor (bank 1 sensor 2) have the same
amplitude (2 trip detection logic)

Three-way catalytic converter

Open or short in (heated) oxygen sensor circuit

(Heated) oxygen sensor
DI1EE-18

FI7132
Engine Speed
2,500 - 3,000 rpm
Idling
IG SW OFF
Warmed up3 min. or soCheckTime (a)(c)
(d)
(b)
FI6514
OX Signal Waveform (Oscilloscope)
1.0 V
0 V
200 m sec. /Division
DI-74
- DIAGNOSTICSENGINE
1996 TERCEL (RM440U)
CONFIRMATION ENGINE RACING PATTERN
(a) Connect the TOYOTA hand-held tester to the DLC3, or connect the probe of the oscilloscope between
terminals OX1, OX2 and E1 of ECM.
(b) Start engine and warm it up with all accessories switched OFF until engine coolant temperature is
stable.
(c) Race the engine at 2,500 - 3,000 rpm for about 3 minutes.
(d) After confirming that the waveform of the oxygen sensor, bank 1 sensor 1 (OX1), oscillate around 0.5
V during feedback to the ECM, check the waveform of the heated oxygen sensor, bank 1 sensor 2
(OX2).
HINT:
If there is a malfunction in the system, the waveform of the
heated oxygen sensor, bank 1 sensor 2 (OX2), is almost the
same as that of the oxygen sensor, bank 1 sensor 1 (OX1), on
the left.
There are some cases where, even though a malfunction ex-
ists, the MIL may either light up or not light up.
INSPECTION PROCEDURE
1 Are there any other codes (besides DTC P0420) being output?
YES Go to relevant DTC chart.
NO
2 Check heated oxygen sensor (bank 1 sensor 2) (See page DI-44).