Experiencing a no-start or rough idle in a vehicle after it’s been sitting hot for a short period? This frustrating issue, often referred to as “hot soak,” can leave drivers stranded and puzzled. As an automotive technician, understanding how to diagnose and resolve this problem efficiently is crucial. This guide will walk you through the process, leveraging the power of diagnostic tools like the CH6000 scan tool, and provide a detailed repair procedure to get vehicles back on the road.
Diagnosing Hot Soak Restart Issues with the CH6000 Scan Tool
The symptoms of a hot soak condition are typically characterized by a no-start, rough idle, or even engine die-out shortly after restarting a hot engine that has been sitting for 10 to 20 minutes. This issue can be exacerbated by modern fuel blends containing alcohol. In some cases, vehicles may refuse to restart until the engine has completely cooled down. The root cause often lies in fuel vapor buildup within the fuel rail.
To accurately diagnose this condition, the CH6000 scan tool, also known as the DRB III, is an indispensable tool. Here’s a step-by-step diagnostic approach:
Initial Checks and Diagnostic Trouble Codes (DTCs)
Begin by using the CH6000 scan tool to check for any Diagnostic Trouble Codes (DTCs) present in the engine and transmission systems. Connect the CH6000 to the vehicle’s diagnostic port and follow the scan tool’s prompts to access the relevant diagnostic menus.
If any DTCs are present, it’s essential to record them and address these fault codes first before proceeding further with diagnosing the hot soak issue. Refer to the vehicle’s service manual and the Ch6000 Scan Tool Manual for guidance on interpreting and resolving specific DTCs.
Fuel Pressure Testing
A critical step in diagnosing hot soak issues is to perform a fuel pressure test. This will help determine if fuel pressure loss is contributing to the problem.
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Cold Soak Preparation: Ensure the vehicle has been cold soaked for a minimum of 8 hours, either outdoors or inside the shop. This ensures accurate test results.
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Connect Fuel Pressure Gauge: Connect a fuel pressure gauge, such as Miller Tool C4799, to the fuel system’s service port. For 2.7L engines, you’ll need to use Miller Tool C4799 along with adapter 6539.
Alt text: Fuel pressure gauge connected to fuel line with adapter on a 2.7L engine for hot soak diagnosis.
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2.7L Engine Specific Steps: For 2.7L engines, perform the fuel bleed procedure as outlined in the service manual. Disconnect the quick connect fuel line at the rear of the engine, just below the throttle body. Connect adapter 6539 to the fuel line and then attach the pressure gauge C4799 to the adapter.
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Monitor Fuel Pressure: With the fuel pressure gauge connected, switch the ignition key to the “run” position (do not start the engine). Observe the fuel pressure gauge and allow the pressure to stabilize, typically around 48 to 50 psi. Once stabilized, switch the ignition key to the “off” position.
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Pressure Drop Monitoring: Carefully monitor the fuel pressure gauge for a period of 15 minutes. Note the amount of pressure drop during this time.
Interpreting Fuel Pressure Results
The fuel pressure drop reading will determine the next course of action:
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Significant Pressure Drop (20 PSI or more): If the fuel pressure drops by 20 PSI or more within 15 minutes, this indicates a likely issue with the fuel pump module. In this case, the fuel pump module will require replacement, along with a PCM flash update as part of the repair procedure.
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Minimal Pressure Drop (Less than 20 PSI): If the fuel pressure drop is less than 20 PSI, the fuel pump module is likely functioning correctly in terms of pressure retention. In this scenario, proceed with only the PCM flash update repair procedure.
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2.7L Engine Additional Checks: For vehicles equipped with a 2.7L engine, regardless of the fuel pressure test results, thermostat modification and heater hose modification procedures are also required as part of the comprehensive repair.
Repair Procedures for Hot Soak Issues
This repair bulletin addresses hot soak no start/rough idle conditions through PCM software updates, potential fuel pump module replacement, and specific modifications for 2.7L engines.
PCM Reflash Procedure Using CH6000 (DRB III)
The core of this repair involves reprogramming the Powertrain Control Module (PCM) with updated software calibrations. The CH6000 scan tool (DRB III) is essential for this procedure.
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Connect MDS and DRB III: Connect the Mopar Diagnostic System (MDS) and the CH6000 (DRB III) scan tool to the vehicle and power them on. Ensure both systems are running the required software versions (Release 21 or higher for MDS, and TIL CD Release 1161 or higher).
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Navigate MDS and DRB III Menus: On the DRB III main menu, select “MDS DIAGNOSTICS.” On the MDS, navigate to “DIAGNOSTIC MENU,” then “VEHICLE CONTROLLER PROGRAMMING,” and finally “PROGRAMMING OF ALL OTHER CONTROLLERS USING MDS & DRB III.” Follow the on-screen prompts on both the MDS and DRB III.
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PCM Part Number Acquisition and Programming: The systems will guide you through obtaining the current PCM part number. The MDS will display the current PCM part number and the appropriate replacement part number if an update is available. Press “NEXT MENU” to initiate programming.
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No Updates Available Message: If the PCM is already updated with the latest software, a “NO UPDATES AVAILABLE” message will appear. Verify the PCM part number on the vehicle against the displayed part number to confirm if the update has been previously applied. If it has, further diagnosis is needed for the hot soak condition.
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Follow Prompts and Complete Programming: Continue to follow the prompts on the MDS and DRB III to complete the PCM reprogramming process.
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Software Update and Modification Labels: After successful reprogramming, it’s crucial to apply the “Authorized Software Update Label” (p/n 04669020) to the PCM and cover it with the clear plastic overlay. Additionally, apply the “Authorized Modification Label” (p/n 04275086) near the Vehicle Emission Control Information (VECI) label.
Alt text: Authorized Software Update Label for PCM reprogramming procedure using CH6000 scan tool.
Alt text: Authorized Modification Label to be placed near VECI label after PCM update with CH6000.
Fuel Pump Module Replacement (If Required)
If the fuel pressure diagnosis indicated a significant pressure drop, fuel pump module replacement is necessary. Refer to the vehicle’s service manual (publication number 81-270-8140) for detailed procedures on fuel pump module replacement. Remember to perform the PCM reflash procedure after replacing the fuel pump module.
2.7L Engine Thermostat and Heater Hose Modifications
For all 2.7L engines, and especially those with engine build codes prior to 04/20/98, additional modifications are required: thermostat modification and heater supply hose modification.
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Thermostat Modification:
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Remove Thermostat: Follow the service manual (publication number 81-270-8140) to remove the thermostat on 2.7L engines. Warning: Exercise extreme caution when working with the cooling system. Never remove the pressure cap when the system is hot and under pressure to prevent serious burns from hot coolant.
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Modify Thermostat Poppet Valve: Press down on the secondary poppet spring of the thermostat. Remove and discard the secondary poppet c-clip and spring.
Alt text: Thermostat modification showing removal of secondary poppet c-clip and spring for 2.7L engine hot soak fix.
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Reinstall Thermostat: Reinstall the modified thermostat into the engine, ensuring the thermostat air bleed is positioned at the 12 o’clock position. Refer to the service manual for proper reinstallation procedures.
Alt text: Thermostat re-installed with air bleed at 12 o’clock position as part of CH6000 scan tool repair procedure.
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Heater Hose Modification:
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Identify Heater Supply Hose Configuration: Identify the vehicle’s heater supply hose configuration. There are two possible configurations (A and B) as shown in Figure 6 of the original bulletin.
Alt text: Heater hose configuration A and B for 2.7L engine modification related to CH6000 scan tool repair.
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Parts Procurement based on Configuration: Obtain the correct heater supply hose and clamps part numbers based on the identified configuration (A or B) as listed in the original bulletin’s parts list.
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Hose Modification and Installation: Follow the detailed steps outlined in the original service bulletin and illustrated in Figure 7 and Figure 8 for cutting, Tee insertion, and hose routing for the heater hose modification. Use new hose clamps to secure all connections.
Alt text: Cutting and Tee insertion point for heater hose modification procedure using CH6000 manual guidance.
Alt text: Final heater hose configuration after modification to resolve hot soak issue, aided by CH6000 scan tool diagnosis.
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Coolant Refill and Air Purge: Refill the cooling system with Mopar long-life coolant (p/n 05011764AB) and strictly adhere to the cooling system fill procedures outlined in the service manual. The system capacity is approximately 8.5 liters (9 quarts). Proper coolant fill is critical for cooling system performance.
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Engine Air Purge: Operate the engine at 2000 to 2300 RPM for 20 minutes to purge any remaining air from the cooling system. The CH6000 scan tool can be used to set the engine RPM within the “engine actuators, RPM set” function. Monitor this procedure periodically as the actuator test has a 5-minute timeout. Use the reset feature to continue the engine RPM actuator feature if needed. Caution: Do not exceed 2500 RPM during the air purge procedure.
Conclusion
Addressing hot soak no start or rough idle conditions requires a systematic approach, leveraging diagnostic tools like the CH6000 scan tool and following detailed repair procedures. By accurately diagnosing the issue and implementing the PCM reflash, potential fuel pump replacement, and specific 2.7L engine modifications, technicians can effectively resolve these problems, ensuring vehicle reliability and customer satisfaction. The CH6000 scan tool manual and vehicle-specific service documentation are invaluable resources throughout this diagnostic and repair process.
