- Identifying Diagnostic Trouble Codes
HOW DIAGNOSTIC TROUBLE CODES (DTC) P135O / P1361 ARE DETERMINEDThe Ignition Control (IC) output circuitry in the Powertrain Control Module (PCM) issues IC output pulses anytime crankshaft reference signal input pulses are being received. When the ignition system is operating in the module mode (no voltage on the bypass control circuit), the ignition control module grounds the IC pulses coming from the PCM. The ignition module will remove the ground path for the IC pulses only after switching to the IC mode. (The PCM commands the switching between module and IC modes, via the bypass control circuit of the ignition control module.) The PCM monitors its own IC output, and expects to see no pulses on the IC circuit when it has not yet supplied the 5 volts on the bypass control circuit. When the second fuel control reference pulse at the start of crank is seen by the PCM, it applies S volts to the bypass control circuit and the IC pulses should no longer be grounded by the ignition module. The PCM constantly monitors its IC output, and should "see" the IC pulses only when operating in the IC mode.
If IC output CKT 423 is open, or shorted to volts or CKT 424 is shorted to voltage, the PCM will detect IC output pulses while attempting to start the engine (in the module mode) due to the ignition control module not being able to ground the IC pulses. Three things will occur: 1. DTC P1350 or P1361 will set, 2. The PCM will not apply 5 volts to the bypass circuit, and 3. The engine will start and run in the module mode.
If IC output CKT 423 is grounded, the PCM would not detect a problem until the change to IC mode is commanded by the PCM. When the PCM applies 5 volts to the bypass control circuit, the ignition control module will switch to the IC mode. With IC CKT 423 grounded, there would be no IC pulses for the ignition control module to trigger the ignition coils, and the engine may falter. The PCM will quickly revert back to the module mode (turn "OFF" the 5 volts on the bypass control), DTC P1361 will set, and the ignition system will operate in the module mode until the fault is corrected and the engine is stopped and restarted.
If bypass control CKT 424 is open -or- grounded, the ignition control module will not switch to the IC mode. In this case, the IC pulses will stay grounded in the ignition control module, and DTC P1361 will be set. The engine will start and run in the module mode.
RESULTS OF INCORRECT OPERATION
An open or ground or short to volts in the IC or bypass circuit will set DTC P1350 or P1361. If a fault occurs in the IC output circuit when the engine is running, the engine may falter or quit running but will restart and run in the module mode once the ignition has been cycled. A fault in either circuit will force the ignition system to operate on module mode timing (10° BTDC), which will result in reduced performance and fuel economy.
The PCM uses information from the engine coolant temperature sensor in addition to RPM to calculate the main spark advance values as follows:
High RPM = more advance
Cold engine = more advance
Low RPM = less advance
Hot engine = less advance
Therefore, detonation could be caused by high resistance in the engine coolant temperature sensor circuit. Poor performance could be caused by low resistance in the engine coolant temperature sensor circuit.
SYSTEM DIAGNOSIS
If the "Engine cranks but will not run" or immediately stalls, CHART A-3 must be used to determine if the failure is in the ignition system or the fuel system. Related Tests, Information and Procedures
If DTC P0321. P0341. P0342 or P135O orP1361 is set, the appropriate diagnostic trouble code chart must be used for diagnosis. Testing and Inspection
If a misfire is being experienced, CHART C-4 will provide a systematic diagnostic procedure. Chart C-4F Misfire