IMPORTANCE OF INFORMATION GATHERING
Diagnosing a transmission malfunction requires gathering as much relevant information as possible before removing the unit from the vehicle. This is particularly crucial when dealing with problematic transmissions, as it helps avoid unnecessary repairs and misdiagnoses.
CASE OVERVIEW
A customer brought in a 2006 Ford F-350 equipped with a 6.0L Direct Injection Turbo Diesel and a 5R110W 4×4 Transmission, reporting a persistent 2-3 shift slip. The issue persisted despite rebuilding the transmission at a nearby shop and installing two different transmissions and two different PCMs. Convinced that defective wiring was the cause, the customer authorized further diagnosis.
VEHICLE INSPECTION
Upon inspection, we noted several modifications, including a modified engine, stock PCM program, two different transmissions and PCMs previously installed, a deep aluminum oil pan, oversized exhaust pipes, and a dual battery setup, with one battery obstructing PCM access. The customer reported a 2-3 shift problem that occasionally neutralized after 15 minutes of driving.
To gather more data, we scanned all modules for codes. The Generic Electronic Module (GEM) codes revealed P1832 (Transfer Case Differential Lockup Solenoid Circuit Fault), P1876 (Transfer Case 2WD Solenoid Circuit Fault), B1318 (Low Battery Voltage at Module), and B1483 (Brake Pedal Input Circuit Fault). The Airbag Module Code showed B1932 (Driver Airbag High Resistance/Circuit Fault), while the Engine Module Code indicated P0401 (EGR Insufficient Flow Detected). No codes were present in the Transmission Module. We installed a pressure transducer on the main line pressure port to further diagnose the issue and connected a scanner to record transmission PID data during a road test.
ROAD TEST FINDINGS
Within five minutes of driving, we experienced a shift flare-bang. The recorded data revealed that the issue was actually a 3-5 shift problem, not a 2-3 shift problem as initially reported. See Figure 1 for notes on our findings.
The transmission contained an aftermarket kit that resulted in higher-than-stock line pressure. The PCM raises line pressure to 175 psi during each shift, but during the 3-5 shift flare, line pressure was raised higher due to higher engine RPM and increased fluid volume. Once the Direct Clutches engaged, the PCM lowered the line pressure as it did for other shifts. See Figure 2.
ADDITIONAL TESTING
We conducted an Alternator Ripple Test to rule out electrical faults, given that we have seen a shorted alternator diode cause electrical problems in previous cases. The test results showed no diode faults. See Figure 3. Next, we performed Electrical Circuit Testing for SSPC C & SSPC D.
SSPC C (Shift Solenoid Pressure Control C) controls the intermediate clutch, where pressure is directly proportional to applied DC amps. SSPC D (Shift Solenoid Pressure Control D) controls direct clutches, where pressure is inversely proportional to applied DC amps. We monitored Channel 1 (Yellow) for the SSPC C average DC voltage, Channel 2 (Green) for the SSPC D average DC voltage, and Channel 3 (Blue) for Main Line Pressure. The conclusion was that no electrical issues were present, confirming that we were dealing with an internal transmission problem (see Figure 4).
TRANSMISSION INSPECTION & REPAIRS
Upon removing and inspecting the transmission, we discovered aftermarket Direct Clutches, a molded piston, and non-factory fluid. To correct the issue, we replaced the Direct Drum molded piston, installed factory-spec Direct Clutches, and refilled the transmission with the factory-recommended fluid.
FINAL RESULTS
After the repair, the 3-5 shift improved significantly, and the shift flare disappeared. Combining a modified engine and transmission created the perfect storm for this issue. While the previous shop had successfully rebuilt 5R110W transmissions, the modifications in this case introduced unique complications.
KEY TAKEAWAY
When dealing with problematic transmissions, always gather as much information as possible before removing the unit. Doing so helps avoid unnecessary repairs and enables a more targeted and efficient diagnosis.
