code 42 refers to the dfi module not receiving the bypass signal from the ecu
so most likely cause would be the plug connector to the dfi module or a faulty dfi module
do you have a friend you can swap dfi with to test
this is the holden diagnostics
circuit 423 is dis pin A
circuit 424 is dis pinB
CIRCUIT DESCRIPTION:
There are two modes of ignition system operation: BYPASS mode, and ELECTRONIC SPARK TIMING mode. The
Bypass mode is normally used while starting the engine, while the Electronic Spark Timing mode is used to allow
the PCM to control the ignition system after the engine is running. The PCM controls a "Bypass control circuit", used
to control the ignition module between the two different ignition system modes.
The PCM's Electronic Spark Timing (EST) output circuitry generates EST output pulses anytime crankshaft
reference input pulses are received. The PCM also monitors it's EST output terminal, to monitor if and when EST
pulses are present.
When the ignition system is operating in the Bypass mode (such as when the engine is cranking), the ignition
module earths the EST pulses coming from the PCM. Because the EST pulses should be earthed through the
ignition module during Bypass mode operation., the PCM should not detect EST pulses on it's EST output terminal.
When the engine is started, the PCM applies 5 volts to the Bypass control circuit. When received by the ignition
module, this 5 volts control causes the ignition module to release the earth from the EST pulses coming from the
PCM. The ignition module will then use the EST pulses to operate the ignition system. When this occurs, the PCM
will correctly detect EST pulses at it's EST output terminal.
If the Bypass control circuit has as open fault or short to earth, or if the EST circuit has a short to earth or short to
voltage, the PCM cannot control the ignition module to release the EST pulses from being earthed. Because the
PCM also monitors it's EST output terminal for EST pulses, if it detects no EST pulses after it has "turned on" the 5
volts to the Bypass control circuit, and the engine speed goes above 1600 RPM, a DTC 42 will be set.
DTC 42 WILL SET IF:
• Engine speed is greater than 1600 RPM.
• PCM has detected no EST output pulses for 200 milliseconds.
TEST DESCRIPTION:
Number(s) below refer to Step numbers on the Diagnostic chart.
4. This step checks to see if circuit 423 is shorted to voltage.
7. This step checks to see if circuit 423 is shorted to earth.
10. This step checks to see if circuit 424 is shorted to earth.
12. This step checks to see if circuit 424 is open.
13 This step checks to see if the ignition module is capable of switching from Bypass to EST mode.
DIAGNOSTIC AIDS:
• Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks,
improperly formed or damaged terminals, and poor terminal to wire connection.
• Damaged Harness. Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the
ignition module, turn the ignition "ON". Connect and observe a voltmeter connected between the Bypass control
circuit and B+, while moving connectors and wiring harness related to the ignition module. A change in voltage
will indicate the location of the fault.
STEP ACTION VALUE YES NO
1. Was the "On-Board
Diagnostic" (OBD) System
Check performed?
Go to Step 2. Go to OBD
System Check.
2. 1. Clear DTC 42.
2. Start engine, and run
above 1600 RPM.
3. Observe DTC(s).
Did DTC 42 set ?
Go to Step 3 DTC 42 is
intermittent. Refer
to "Diagnostic
Aids" above.
3. 1. Ignition "OFF".
2. Disconnect ignition
module 14 pin
connector.
3. Probe ignition module
harness connector
terminal "A" with a
voltmeter to earth.
4. Ignition "ON".
Is voltage greater then the
specified value?
0.5 V Go to Step 4 Go to Step 6
4. 1. Ignition "OFF".
2. Disconnect PCM
connectors.
3. Ignition "ON".
Is voltage still present at
ignition module harness
connector terminal "A" ?
Go to Step 5 Go to Step 15
5. Repair short to voltage on
circuit 423.
Is action complete ?
Verify Repair
6. 1. Ignition "ON".
2. Probe ignition module
harness connector
circuit 423 with a test
light connected to
battery voltage.
Is test light "ON" ?
Go to Step 7 Go to Step 9
7. 1. Ignition "OFF
2. Disconnect PCM
connectors.
3. Probe ignition module
connector circuit 423
with a test light
connected to battery
voltage.
Is test light "ON" ?
Go to Step 8 Go to Step 14
8. Repair short to earth in
circuit 423.
Is action complete
Verify Repair
9. 1. Ignition "ON".
2. Disconnect ignition
module 14 pin
connector.
3. With test light
connected to battery
voltage, probe ignition
module harness
connector circuit 424.
Is test light "ON" ?
Go to Step 10 Go to Step 12
STEP ACTION VALUE YES NO
10. 1. Ignition "OFF".
2. Disconnect PCM
connectors.
3. Ignition "ON".
4. Disconnect ignition
module 14 pin
connector.
5. With test light
connected to battery
voltage, probe ignition
module harness
connector circuit 424.
Is test light "ON" ?
Go to Step 11 Go to Step 14
11. Repair short to earth on
circuit 424.
Is action complete ?
Verify Repair
12. 1. Ignition "OFF".
2. Disconnect PCM
connectors.
3. Check for faulty
connection or open
circuit 424.
Is fault found ?
Verify Repair Go to Step 13
13. 1. Ignition "OFF".
2. Reconnect ignition
module 14 pin
connector.
3. Disconnect PCM
connectors.
4. Ignition "ON".
5. Probe PCM harness
connector circuit 423
with an ohmmeter
connected to earth.
5. Probe PCM harness
connector circuit 424
with a test light
connected to battery
voltage.
NOTE:
As the test light contacts
circuit 424, does
resistance switch from
under specified value to
over specified value?
300
ohms
to
6000
ohms
Go to Step 14 Go to Step 15
14. Replace PCM.
Refer to Section 6C1-3
Service Operations, for
PCM Security Link
procedure.
Is action complete?
Verify Repair
15. Replace ignition module.
Is action complete ?
Verify Repair