Case IH 52 – Transmission ECM: Transmission Temperature Sender (Bb) Short Circuit

The ECM detects that the voltage has dropped below 0.34 volts at ECM connector 2, pin 25, indicating the circuit is shorted to ground, the sender has failed, or the transmission oil temperature is critically high (above 130°C / 266°F). This causes the transmission to enter Auto Mod, resulting in sluggish operation and higher clutch pedal inching.

• JXC
• TN55
• TN65
• TN70
• TN75
• TNDA
• TNSA

1. 1

   Verify that the transmission oil is not actually overheating (above 130°C / 266°F)

2. 2

   Check Diagnostic Channels: Access channel H9, channel 2 (should read below 70 counts)

3. 3

   Check Diagnostic Channels: Access channel H5 (will not show 'd29' if the Transmission Temperature Sender is disconnected)

4. 4

   Check Diagnostic Channels: Access channel HC (verify that it is not showing an accurate temperature)

5. 5

   Test for a short to ground in the wiring between ECM connector 2, pin 25 and the Transmission Temperature Sender

6. 6

   Test for a short across the sender terminals themselves

7. 7

   Test for a short in the wiring between the Transmission Temperature Sender and ECM connector 2, pin 29

1. 1

   Disconnect the Sender

   Unplug the Transmission Temperature Sender (Bb) to see if the voltage reading at the ECM changes. If the short goes away, the sender is internally shorted.

2. 2

   Inspect the Harness

   Visually and electrically inspect the wiring harness from the sender back to ECM connector 2 (specifically pins 25 and 29). Look for rubbed-through insulation causing a ground short.

3. 3

   Repair Wiring

   If a short is found in the harness, repair or replace the damaged section of the wiring.

4. 4

   Replace the Sender

   If the wiring tests good but the voltage at pin 25 remains below 0.34 volts when plugged in, replace the faulty Transmission Temperature Sender.

5. 5

   ECM Replacement

   If the sender is new, the wiring is completely intact with no shorts, and the code persists, the ECM itself is faulty and must be replaced.