Diagnostic Aids

Perform this test only when instructed during QUICK TEST or if directed by other test procedures. This test is only intended to diagnose the following:

• Supercharger (Boost) By-Pass Solenoid (Service Part Name Is: Thermactor Air Control Solenoid/Vacuum Valve Assembly)
• Vacuum Reservoir Assembly. See Fig 1.
• Vacuum Hoses/Tubes
• Wiring Harness Circuits (SCB, PWR GND & VPWR)
• Powertrain Control Module (PCM)
• Supercharger Assembly (Including Supercharger By-Pass Actuator)

Fig 1: Supercharger System Vacuum Diagram

Courtesy of FORD MOTOR CO.

NOTE: Supercharger is by-passed when brakes are on and throttle is in wide open position. This condition causes excessive engine torque and is referred to as brake torque. If possible, check with vehicle owner to determine if engine has been subjected to a brake torque condition causing DTC P0234 to set.
1. 1) DTC P0234: Check For Other DTCs
   DTC P0234 is set and PCM disables supercharger boost to keep from damaging engine or transmission during potentially harmful operating conditions. Possible causes are.
   • Brake Torque Condition (Brake Pedal Applied & Throttle At Wide Open)
   • Transmission Oil Temperature Exceeds Calibrated Threshold
   • Engine Overheating
   • Ignition Misfire Exceeding Calibrated Threshold
   • Knock Sensor Failure Or Knock Detected
   • Low Speed Fuel Pump Relay Not Switching

   If engine is a no-start, go to TEST A, step 1) . If engine starts and then stalls, diagnose by symptom. Go to SYMPTOMS in TROUBLE SHOOTING - NO CODES - EEC-V - CNG & GASOLINE article. If engine starts and does not stall, road test vehicle 10-15 minutes with engine speed exceeding 2000 RPM. Ensure engine is at normal operating temperature and that upper radiator hose is hot and pressurized. Repeat QUICK TEST and check for KOEO, KOER and continuous memory DTCs. If any other DTCs are present with DTC P0234, service other DTCs before continuing with this test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS table. If only DTC P0234 is present, go to next step.

2. 2) Check PIDs For Causes Of Overboost Condition
   
   Start engine and allow to idle. Using scan tool, select IAT2, TFT and RPM PIDs from PID/DATA MONITOR & RECORD menu. If IAT2 PID value is more than 230°F (110°C), check for low fluid level in intercooler system. Check for cracked intercooler lines. Repair as necessary. If TFT PID value is more than 275°F (135°C), check for low transmission fluid level. Check for transmission leaks. Repair as necessary. If IAT2 PID value is 230°F (110°C) or less and if TFT PID value is 275°F (135°C) or less, go to next step.
3. 3) Check For Low Speed Fuel Pump Relay Not Switching
   
   Start engine and allow to idle. Using scan tool, select LFPF PID from PID/DATA MONITOR & RECORD menu. If LFPF PID value indicates YES (fault present), go to TEST KA, step 45) and/or 60) and perform diagnostics for DTC P1232. If LFPF PID value indicates NO (no fault present), cause of overboost condition is unable to be determined at this time. Check for engine knock while driving vehicle. Repair as necessary. If engine knock is not present, ensure vehicle owner has an understanding of a brake torque condition and that brake torque can result in transmission damage.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 3) to step 6). No test procedures have been omitted.
4. 6) DTC P0243: Check Supercharger (Boost) By-Pass Solenoid Output
   
   Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Disconnect Supercharger (Boost) By-Pass (SCB) solenoid connector. Connect a test light between SCB solenoid harness connector terminals. See Fig 2. Turn ignition switch to ON position. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE under ADDITIONAL SYSTEM FUNCTIONS. Attempt to cause SCB solenoid driver in PCM to close and open by commanding ALL OUTPUTS ON, then OFF. Observe test light while cycling ALL OUTPUTS ON, then OFF. If test light turns on then off, go to next step. If test light stays off, go to step  8). If test light stays on, go to step  11).
   Fig 2: Identifying Supercharger (Boost) By-Pass Solenoid Wiring Harness Connector Terminals

   Courtesy of FORD MOTOR CO.
5. 7) Check SCB Solenoid Resistance
   
   Using a DVOM, measure resistance between SCB solenoid terminals. If resistance is not 68-78 ohms, replace SCB solenoid. If resistance is 68-78 ohms, check for damaged vacuum hoses between intake manifold and SCB solenoid. Check for vacuum reservoir leaks. Repair or replace as necessary. If no faults are found, go to TEST Z, step  1) and check for intermittents.
6. 8) Check For Open VPWR Circuit Between SCB Solenoid & PCM Power Relay
   
   Using a DVOM, measure voltage between negative battery terminal and SCB solenoid harness connector VPWR terminal. See Fig 2. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, repair open in VPWR circuit between SCB solenoid and PCM power relay.
7. 9) Check VPWR Circuit For Open In Harness
   
   Turn ignition switch to OFF position. Disconnect PCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Using a DVOM, measure resistance of VPWR circuit between PCM harness connector and SCB solenoid harness connector. See Figure and Fig 2 . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in VPWR circuit.
8. 10) Check SCB Circuit For Open In Harness
   
   Using a DVOM, measure resistance of SCB circuit between PCM harness connector and SCB solenoid harness connector. If resistance is less than 5 ohms, replace PCM. If resistance is 5 ohms or more, repair open in SCB circuit.
9. 11) Check SCB Circuit For Short To PWR GND Or Chassis Ground In Harness
   
   Turn ignition switch to OFF position. Disconnect scan tool from DLC. Disconnect PCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Using a DVOM, measure resistance between PCM harness connector terminal No. 42 (SCB) and terminals No. 51, 77, 103 (PWR GND), and chassis ground. If all resistance measurements are more than 10 k/ohms, go to next step. If any resistance measurement is 10 k/ohms or less, repair SCB circuit for short to ground or PWR GND. See WIRING DIAGRAMS article.
10. 12) Check SCB Circuit For Short To VPWR Or VREF In Harness
    
    Turn ignition switch to ON position. measure voltage between negative battery terminal and PCM harness connector terminal No. 42 (SCB). If voltage is less than one volt, replace PCM. If voltage is one volt or more, repair SCB circuit for short to VPWR or VREF circuit. See WIRING DIAGRAMS article.
NOTE: Step  13) is performed when directed here from SYMPTOMS in TROUBLE SHOOTING - NO CODES - EEC-V - CNG & GASOLINE article.
11. 13) Lack Of Power (Low Boost): Check Vacuum Hoses
    Check vacuum hoses for cracks, bends, kinks, leaks or being disconnected between the following areas:
    • Supercharger by-pass actuator and supercharger by-pass solenoid.
    • Supercharger by-pass solenoid and vacuum reservoir assembly.

    Repair or replace component(s) as necessary. If no problems are found, return to LACK/LOSS OF POWER diagnostics under SYMPTOMS in TROUBLE SHOOTING - NO CODES - EEC-V - CNG & GASOLINE article.