Pinpoint Test V: Dual Generator Lower Fault Detected (P1148)
Pinpoint Test
Pinpoint Test V: Dual Generator Lower Fault Detected (P1148)
Refer to Wiring Diagram Set 12, Charging System for schematic and connector information. Diagrams By Number
Normal Operation
The generator output is determined by the voltage of the A circuit. The A circuit voltage is compared to a set voltage internal to the voltage regulator and the voltage regulator controls the generator field current to maintain the correct generator output. The set voltage varies with temperature and is typically higher in cold temperatures and lower in warm temperatures.
This pinpoint test is intended to diagnose the following:
- Lower generator disconnected
- B+ circuit fusible links
- B+ circuit (lower) open
- A circuit open, short to ground or high resistance
- I circuit open or short to ground
- Lower generator
PINPOINT TEST V: DUAL GENERATOR LOWER FAULT DETECTED (P1148)
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V1 CHECK THE LOWER GENERATOR CONNECTIONS
- Ignition OFF.
- Disconnect: Lower Generator C1251a, C1251b.
- Check the lower generator connectors for damage and correct connection.
- Connect: Lower Generator C1251a, C1251b.
- Are the lower generator connectors OK and correctly connected?
Yes
GO to V2.
No
REPAIR the connectors as necessary. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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V2 CHECK THE LOWER GENERATOR B+ VOLTAGE
- Measure the voltage between the B+ terminal C1251b of the lower generator and ground.
- Is the voltage equal to battery voltage?
Yes
GO to V3.
No
CHECK the B+ circuit SDC02 (RD) including the fusible links. REPAIR as necessary. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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V3 CHECK THE LOWER GENERATOR A CIRCUIT
- Disconnect: Lower Generator C1251a.
- Measure the voltage between the lower generator C1251a-3, A circuit SBB41 (RD), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
GO to V4.
No
CHECK the lower generator A circuit SBB41 (RD) including the fusible links. REPAIR as necessary. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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V4 CHECK THE LOWER GENERATOR I CIRCUIT CDC47 (WH) FOR VOLTAGE
- Start the engine and wait at least 2 minutes for the glow plugs to stop cycling.
- NOTE: If the glow plug system is cycling, the PCM will not provide voltage on the lower generator I circuit.
- With the Key ON Engine OFF (KOEO), measure the voltage between the lower generator C1251a-1, circuit CDC47 (WH), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
GO to V6.
No
GO to V5.
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V5 CHECK THE LOWER GENERATOR I CIRCUIT 1185 (YE) OR CDC47 (WH) FOR AN OPEN OR A SHORT TO GROUND
- Ignition OFF.
- Disconnect: PCM C1381e.
- Measure the resistance between the lower generator C1251a-1, I circuit CDC47 (WH), harness side and the PCM C1381e-4, circuit 1185 (YE), harness side; and between the lower generator C1251a-1, I circuit CDC47 (WH), harness side and ground.
- Is the resistance less than 5 ohms between the generator and the PCM, and greater than 10,000 ohms between the generator and ground?
Yes
GO to V7.
No
REPAIR the I circuit CDC47 (WH) or 1183 (WH/YE). CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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V6 CHECK THE LOWER GENERATOR VOLTAGE
- Disconnect: Upper Generator C1104a.
- Connect: Lower Generator C1251a.
- Start the engine.
- NOTE: After starting the engine, wait at least 2 minutes for the glow plugs to stop cycling. If the glow plug system is cycling, the PCM will not provide voltage on the lower generator I circuit.
- With the engine running, measure the voltage at the battery(s).
- Is the voltage greater than 13 volts?
Yes
GO to V7.
No
INSTALL a new lower generator. REFER to Generator - Diesel Engines, Dual Generators . CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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V7 CHECK FOR CORRECT PCM OPERATION
- Disconnect all of the PCM connectors.
- Check for:
- corrosion.
- pushed-out pins.
- Connect all of the PCM connectors and make sure they seat correctly.
- Operate the system and verify the concern is still present.
- Is the concern still present?
Yes
INSTALL a new PCM. REPEAT the self-test. TEST the system for normal operation.
No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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