Generac Power Systems GP Series Diagnostic Repair Manual page 56

Section 5 Engine Diagnostic Tests
In the event of a fault, test the sensor using the following
method:
Use needle type back probes to verify Wire 820G
1.
is grounded to the main ground point on the
engine.
• If Wire 820G is not grounded, test and inspect the
harness for breaks and inspect the ECM connector
for damaged pins.
Test wire 820A to ground for 4.5–5 VDC when the
2.
ECM is active.
•
If Wire 820A does not have voltage present when
the ECM is active, test and inspect the harness for
breaks and inspect the ECM plug for damaged
pins.
Determine which output circuit is faulty, Wire 754,
3.
Wire 752, or Wire 766. Test each wire to ground for
output voltage when the ECM is active. A reading
of 0.5–4.5 VDC should be measured.
• If no or low voltage is measured remove and
inspect the sensor. TTMAP voltage should be
between 2.4–2.6 VDC with sensor removed from
system and still connected to harness. Replace as
necessary.
Test 32 – Troubleshooting Ignition
System Faults
(Fault codes 4-1, 4-2 Cylinder 1 /
4-3, 4-4 Cylinder 2)
The ignition system on the 816cc engine is controlled by
the ECM. There are two ignition coils (IC 1 and IC 2). The
coils are powered by the main power relay (MPR) and
fuse F2. The MPR is controlled by the ECM.
In order to generate a fault the following conditions may
apply:
• The ECM will check if ignition coil current is above
the threshold, when the coil is firing.
• The ECM will check if ignition coil current is below
the threshold, when the coil is firing.
•
The ECM will check if ignition coil current is
detected when the coils are not firing.
IC1
IC2
Figure 5-97. Ignition Coils IC1 and IC2
Before troubleshooting is performed check spark plug
wires for fit and condition. Check each coil connector for
12 VDC on Wire 14C. Check the F2 fuse to see if it is
blown or missing or if the relay (IR) is not operational. If
the relay is not operational, or the fuse is blown, the
ignition system will indicate an ignition fault.
50
A B C
451 ECM-4M
14C SPLICE 5
A B C
452 ECM-1M
14C SPLICE 5
015049
Testing Ignition Coil
To test an ignition coil, disconnect the electrical
connection and the primary wire from the coil.
NOTE: It may be necessary to remove the coil from the
valve cover.
Primary resistance (measured
through coil pins 14C and 451–452
Secondary resistance (451–452
measured from spark plug end to
any primary coil terminal)
Test 33 – Troubleshooting Oxygen
Sensor (OS) System Faults
2-1, 2-2)
The oxygen sensor (OS) operates by measuring the
difference in oxygen between exhaust gas and external
air (sample air). A voltage is generated based on the
difference between the two. The oxygen sensors output
is on Wire 804 and Wire 820G. A high voltage (~0.6–0.9
V) indicates a rich condition (low oxygen content) in the
exhaust flow, and a low voltage (~0.1–0.4 V) indicates a
lean condition (high oxygen content) in the exhaust. Wire
607 and Wire 14C are for the OS heater circuit. The
heater maintains the OS temperature allowing the OS to
achieve better accuracy.
OS
A B C D
Figure 5-98. Oxygen Sensor OS
Procedure
Locate and disconnect the oxygen sensor. Keep it
1.
accessible for the duration of this testing proce-
dure.
Set a DMM to measure resistance.
2.
Connect one meter test lead to terminal A of the
3.
sensor and the other meter test lead to terminal B.
Measure and record the resistance.
a. If the DMM indicated INFINITY, replace sensor.
b. If the DMM indicated approximately 15–21 ohms
of resistance, proceed to Step 4.
NOTE: OS resistance at ambient temperature is15–21
ohms. Resistance may read higher if unit was running
prior to troubleshooting.
Connect a resistive load bank to the unit.
4.
Set the DMM to measure DC voltage.
5.
0.85–1.2 Ohm
11.5–18 k Ohm
(Fault Codes
5
14C 14C
14C
14C
14C
607
804
820G
2
820G
820G 820G
Diagnostic Repair Manual
IC1-A
IC2-A
OPS-1
SPLICE 3
ECM-2F
ECM-4J
ECM-4K
EHT-2
TTMAP-3
015050