Vehicle: 2008 Dodge Grand Caravan, V6-3.8L
Problem: The repair shop rebuilt the Grand Caravan’s automatic transmission. After the repairs, the transmission would intermittently slip in third and fourth gears. The technician checked the ATF level and found that it was two quarts over-filled. After setting the fluid to the correct level, the issue remained. A quick scan revealed the following diagnostic trouble codes (DTCs):
P0733 GEAR RATIO ERROR IN 3rd gear
P0734 GEAR RATIO ERROR IN 4th gear
P0792 COMPOUNDER SPEED RATIO ERROR
Details: The Tech-Assist consultant advised checking the harness connection at the transmission because over-filling the oil capacity can cause oil to wick past the seals and foul the electrical circuits, which can cause intermittent problems and DTCs. The technician was further advised to monitor the perimeter identification data (PID) values for the input, transfer, output speed and engine speed sensors to identify any implausible data values.
While monitoring the input speed (turbine) sensor and engine speed PIDs, the input speed exceeded engine speed. Because the engine speed should never exceed the turbine speed, the wiring at the transmission was closely inspected. The technician found excessive oil in the connector, so he also inspected the internal harness. He found that multiple wires were overheated and burnt
Confirmed Repair: After replacing the internal harness, the DTCs were cleared and the transmission was refilled to specification. After taking the vehicle on a lengthy test drive, no DTCs or slippage problems were noted. Fixed!