P050B

P050B-COLD START IGNITION TIMING PERFORMANCE





For a complete wiring diagram consult Diagrams/Electrical.

Theory of Operation


Spark adjustment during a cold start is intended to provide quick response to idle speed variations. The PCM monitors spark advance on a cold start over a period of time, then compares the average spark advance to a threshold.

- When Monitored:
During a cold start condition, with the difference between the AAT and ECT at startup below 10° C, and the engine running at idle.

- Set Condition:
The PCM detects that engine speed is 50 RPM or more (depending on vehicle specifications) below target idle speed for more than 3 seconds, and the average spark advance is above the failure threshold for more than the specified limit. Two trip fault. Three good trips to turn off the MIL.







Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Initial Inspection and Diagnostic Overview.


Diagnostic Test


1. ACTIVE DTC

NOTE: Low battery voltage can cause excessive current draw in very hot and very cold ambient temperatures. Look closely at the temperatures at which this DTC set and make sure the battery can pass a load test before continuing.


NOTE: Diagnose and repair any other DTCs set in the PCM before proceeding with this test.

Turn the ignition on.
With the scan tool, select View DTCs and review the DTC environmental information.
Is the good trip counter greater than 0?

Yes


- The DTC is not active at this time. Refer to the *CHECKING FOR AN INTERMITTENT DTC Diagnostic Procedure.Checking For An Intermittent DTC


No


- Go to 2




2. THROTTLE PLATE INSPECTION
Turn the ignition off.
Remove the air cleaner assembly.
Check for any signs of a foreign material (ice, dirt, or excessive carbon build up) on the throttle plate or in the bore causing the throttle plate to stick.
Were any problems found?

Yes


- Remove the debris if possible or replace the Throttle Body. Disconnect the battery when replacing the Throttle Body. After installation is complete, use a scan tool and perform the ETC RELEARN function.
- Perform the PCM Verification Test.Powertrain Verification Test


No


- Go to 3




3. DIRTY AIR FILTER
Remove and inspect the air filter.
Were any problems found?

Yes


- Replace the air filter.
- Perform the PCM Verification Test.Powertrain Verification Test


No


- Go to 4




4. CONTAMINATED FUEL
Inspect the fuel for contamination. (dirt, water, or other foreign material)
Were any problems found?

Yes


- Drain the fuel from the fuel tank into an approved gas holding tank and add clean fuel. Procedures


No


- Go to 5




5. EXCESSIVE RESISTANCE IN THE (K124) ETC MOTOR (+) CIRCUIT
Turn the ignition off.

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 along with the #8815-1 to perform the diagnosis.

Using a voltmeter, perform a voltage drop test by backprobing the (K124) ETC Motor (+) circuit at the Throttle Body harness connector and by probing the appropriate terminal of the special tool #8815. Make sure the voltmeter leads are connected so that positive polarity is displayed on the voltmeter.

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.

Start the engine.
Is the voltage below 0.5 volts?

Yes


- Go to 6


No


- Repair the (K124) ETC Motor (+) for excessive resistance.
- Perform the PCM Verification Test.Powertrain Verification Test




6. EXCESSIVE RESISTANCE IN THE (K126) ETC MOTOR (-) CIRCUIT
Turn the ignition off.

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 along with the #8815-1 to perform the diagnosis.

Using a voltmeter, perform a voltage drop test by backprobing the (K126) ETC Motor (-) circuit at the Throttle Body harness connector and by probing the appropriate terminal of the special tool #8815. Make sure the voltmeter leads are connected so that positive polarity is displayed on the voltmeter.

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.

Start the engine.
Is the voltage below 0.5 volts?

Yes


- Go to 7


No


- Repair the (K126) ETC Motor (-) for excessive resistance.
- Perform the PCM Verification Test.Powertrain Verification Test




7. THROTTLE BODY
Turn the ignition off.
Disconnect special tool #8815-1 from the C2 PCM harness connector.

NOTE: Use special tool #8815 to avoid possible damage to the Throttle Body harness connector.

Measure the resistance of the ETC Motor by probing the appropriate terminals of special tool #8815 for the (K124) ETC Motor (+) circuit and the (K126) ETC Motor (-) circuit.
Is the resistance between 2.5 and 25 ohms at closed throttle?

Yes


- Go to 8


No


- Replace the Throttle Body. Disconnect the battery when replacing the Throttle Body. After installation is complete, use a scan tool and perform the ETC RELEARN function.
- Perform the PCM Verification Test.Powertrain Verification Test




8. POWERTRAIN CONTROL MODULE (PCM)
Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Throttle Body and the Powertrain Control Module (PCM).
Look for any chafed, pierced, pinched, or partially broken wires.
Look for broken, bent, pushed out or corroded terminals.
Search for any Technical Service Bulletins that may apply.
Were any problems found?

Yes


- Repair as necessary.
- Perform the PCM Verification Test.Powertrain Verification Test


No


- Replace the Powertrain Control Module (PCM).
- Perform the PCM Verification Test.Powertrain Verification Test