2001 TOYOTA PRIUS Service Repair Manual

EM±2
± ENGINE MECHANICALCO/HC
111 8 Author: Date:
2001 PRIUS (RM778U)
If the CO/HC concentration does not comply with regulations,
troubleshoot in the order given below.

Check heated oxygen sensor operation.
(See page DI±44)

See the table below for possible causes, and then inspect
and correct the applicable causes if necessary.
COHCProblemsCauses
NormalHighRough idle1. Faulty ignitions:

Incorrect timing

Fouled, shorted or improperly gapped plugs

Open or crossed high±tension cords
2. Incorrect valve clearance
3. Leaky intake and exhaust valves
4. Leaky cylinders
LowHighRough idle
(Fluctuating HC reading)1. Vacuum leaks:

PCV hoses

Intake manifold

Throttle body
2. Lean mixture causing misfire
HighHighRough idle
(Black smoke from exhaust)1. Restricted air filter
2. Plugged PCV valve
3. Faulty EFI systems:

Faulty pressure regulator

Defective water temperature sensor

Defective air flow meter

Faulty ECM

Faulty injectors

Faulty throttle position sensor
NormalHigh1. Faulty HCAC:

Faulty VSV

Faulty actuator

EM1IT±02
F12396
TOYOTA Hand±held
Tester
DLC3
A13923
± ENGINE MECHANICALCOMPRESSION
EM±3
111 9 Author: Date:
2001 PRIUS (RM778U)
COMPRESSION
INSPECTION
HINT:
If there is lack of power, excessive oil consumption or poor fuel
economy, measure the compression pressure.
NOTICE:
The measurement of compression pressure should be per-
formed in the Cranking Mode.
1. WARM UP AND STOP ENGINE
Allow the engine to warm up to normal operating temperature.
2. REMOVE AIR CLEANER ASSEMBLY
3. REMOVE IGNITION COIL (See page IG±6)
4. REMOVE SPARK PLUGS
5. CONNECT TOYOTA HAND±HELD TESTER
(a) Connect the TOYOTA hand±held tester to the DLC3.
(b) Select the cranking mode on the TOYOTA hand±held tes-
ter.
(c) Please refer TOYOTA hand±held tester operato's manual
for further details.
6. INSPECT CYLINDER COMPRESSION PRESSURE
(a) Insert a compression gauge into the spark plug hole.
(b) Fully open the throttle.
(c) While cranking the engine, measure the compression
pressure.
HINT:
In the Cranking Mode, the engine speed is automatically con-
trolled at 250 rpm and the throttle valve is also automatically set
in fully±opened condition.
(d) Repeat steps (a) through (c) for each cylinder.
NOTICE:
This measurement must be done in as short a time as pos-
sible.
Compression pressure:
728 kPa (7.4 kgf/cm
2, 106 psi)
Minimum pressure:
534 kPa (5.4 kgf/cm
2, 77 psi)
Difference between each cylinder:
98 kPa (1.0 kgf/cm
2, 14 psi) or less

EM±4
± ENGINE MECHANICALCOMPRESSION
1120 Author: Date:
2001 PRIUS (RM778U)
(e) If the cylinder compression in one more cylinders is low,
pour a small amount of engine oil into the cylinder through
the spark plug hole and repeat steps (a) through (c) for
cylinders with low compression.

If adding oil helps the compression, it is likely that
the piston rings and/or cylinder bore are worn or
damaged.

If pressure stays low, a valve may be sticking or
seating is improper, or there may be leakage past
the gasket.
7. REINSTALL SPARK PLUGS
8. REINSTALL IGNITION COIL (See page IG±7)

EM169±02
A11244
A11245
Timing Marks
A11218
1
3
21
3
2
11
A11219
3
2
3
2
44
44
± ENGINE MECHANICALVALVE CLEARANCE
EM±5
1121 Author: Date:
2001 PRIUS (RM778U)
VALVE CLEARANCE
ADJUSTMENT
HINT:
Inspect and adjust the valve clearance when the engine is cold.
1. REMOVE CYLINDER HEAD COVER
(See page EM±15)
2. SET NO.1 CYLINDER TO TDC/COMPRESSION
(a) Turn the crankshaft pulley, and align its groove with the
timing mark º0º of the timing chain cover.
(b) Check that both timing marks on the camshaft timing
sprocket and valve timing controller assembly are facing
right upas shown in the illustration.
If not, turn the crankshaft 1 revolution (360°) and align the
marks as above.
3. INSPECT VALVE CLEARANCE
(a) Check only the valves indicated.

Using a feeler gauge, measure the clearance be-
tween the valve lifter and camshaft.

Record the out±of±specification valve clearance
measurements. They will be used later to determine
the required replacement adjusting shim.
Valve clearance (Cold):
Intake
0.17 ± 0.23 mm (0.007 ± 0.009 in.)
Exhaust
0.27 ± 0.33 mm (0.011 ± 0.013 in.)
(b) Turn the crankshaft 1 revolution (360°) and align the mark
as above. (See procedure in step 2)
(c) Check only the valves indicated as shown. Measure the
valve clearance. (See procedure in step (a))