Powertrain Controls - ECM/PCM

DTC 23 Chart (1 Of 2):

DTC 23 Chart (2 Of 2):

Ignition Control (IC) Circuit(s):

CIRCUIT DESCRIPTION
The Ignition Control (IC) module sends spark reference and fuel control signals to the PCM. When the engine speed is below about 400 RPM (cranking engine), the IC module controls the spark timing. When the spark timing is controlled by the IC module (module mode), there is no voltage applied to the bypass or Ignition Control (IC) signal circuits. If the PCM detects voltage on the IC signal CKT 423 when the engine speed is below about 400 RPM, DTC 23 will set. When the engine speed exceeds about 100 RPM and at least 16 fuel reference pulses are detected by the PCM, the PCM applies 5 volts to the bypass CKT 424 to switch the spark timing to PCM controlled. When the IC module detects voltage on bypass circuit, it applies voltage to the IC signal to switch from module mode to PCM controlled spark timing mode. If the PCM applies voltage to the bypass circuit and the IC module does not switch to PCM controlled spark timing, DTC 23 will set.

DTC 23 WILL SET WHEN
- DTC 35 is not set.
- Engine speed is below about 400 RPM and PCM detects voltage on the IC signal circuit.
OR
- PCM does not detect voltage on IC signal circuit when engine speed exceeds about 400 RPM for at least 16 fuel reference pulses have been detected by PCM.

ACTION TAKEN (PCM WILL DEFAULT TO)
- With a current DTC 23 set, the PCM will illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon).
- The PCM controlled spark timing will be disabled.

DTC 23 WILL CLEAR WHEN
The fault no longer exists and the ignition switch is cycled "OFF" and "ON."

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Check if DTC 35 is set because a REF LO problem can cause other ignition problems.
2. Checking to see if DTC 23 was set during "CRANK" or while engine was running.
3. Checking if there is a short to voltage on CKT 424 or if a PCM failure is causing the ignition control system to be in bypass spark control when it should not be.
4. Checking to see if there is an open in CKT 423 that is causing no ignition control pulses to reach the ignition control module or if pulses are reaching the ignition control module and it is doing nothing with them.
5a. Checking for a short to voltage on CKT 424.
5b. Checking if bypass control is being sent by the PCM to the ignition control module. If bypass control is being sent the voltage will be greater than 4.1 volts.
6. Checking if bypass control being sent by the PCM is being received by the ignition control module. If CKT 424 is good, resistance will be less than 5 ohms.
7. Checking if PCM is providing proper signal to the 1CM. If PCM terminal "3F3" has between 30 and 100 Hertz, the PCM is not at fault.
8. Checking if PCM can produce the proper ignition control pulses. If max voltage exceeds 3.7 volts, the PCM is OK and the 1CM is at fault.
9. Checking CKT 424 for a short to ground.
10. Checking if the 1CM is able to recognize a bypass signal. If it does, DTC 23 will not set again. If DTC 23 resets the ICM is faulty, if it does not reset the PCM is faulty.
11. Checking if ICM is causing incorrect voltage or if PCM is supplying incorrect signal.

DIAGNOSTIC AIDS
The Tech 1 scan tool does not have any ability to help diagnose a DTC 23 problem.
Refer to Intermittents in Diagnosis by Symptom. - Intermittent Malfunctions

Ignition control line
When CKT 423 is shorted to voltage or open during crank, will set DTC 23 also if CKT 424 is shorted to voltage during crank DTC 23 will set.

Bypass line
During engine run operation, if CKT 424 opens or shorts to ground DTC 23 will set.