P0731 on a 2014-2018 Jeep Cherokee: Check Fluid Level and TCM Software First

P0731 means the transmission control module (TCM) found first gear running outside its allowed ratio on this 9-speed Jeep Cherokee. Start with fluid level and condition, then make sure the TCM software is current. If the code comes back, the valve body and clutch C are next. Shifting can change once the fault is stored, so stop driving if it drops into neutral or you lose drive.

What does P0731 mean on a 2014-2018 Cherokee?

P0731 (Gear 1 Shift Incorrect Ratio) is a TCM code on the 948TE. The TCM compares input shaft speed against output shaft speed and checks the actual ratio against a minimum and a maximum calibrated ratio for the gear. It runs that check in a fixed gear, while a gear engages and during shifts. First gear is 4.70:1.

The TCM runs the monitor only when all of these hold:

• The selector is in Drive or Reverse.
• Fluid temperature is above a calibrated threshold.
• No clutch slip control function is commanded.
• Input speed is above a calibrated threshold and its signal has no failure.
• A valid output speed signal exists, from the output speed sensor or calculated from wheel speed if the sensor signal is not available.
• A valid engine speed signal comes from the PCM.
• During shifts only, output speed and its gradient are both above calibrated thresholds.

The TCM logs a symptom in these cases:

• During a shift, when the measured ratio falls outside the allowed range.
• In a fixed gear with output speed above a threshold, when the ratio stays outside the range for a calibrated time.
• In a fixed gear with output speed below that threshold, when the difference between (output speed times the fixed ratio of the actual gear) and input speed exceeds a threshold for a calibrated time.

If the symptom shows up on an upshift, or on a downshift that needs a dog clutch, the TCM aborts the shift and returns to the gear it started from. On a dog clutch downshift, a fault code naming that dog clutch is stored as well.

In a fixed gear, the TCM answers a symptom by commanding an upshift. After a calibrated number of symptoms it stores the failure and engages a calibrated gear. That gear is monitored too; if it fails, the TCM picks another in a calibrated order meant to steer around the damaged clutch. A further symptom in the last alternative gear stores a general transmission ratio malfunction. Every limit here is a calibrated value inside the TCM.

Read the rest of the gear ratio family too: P0729 (gear 6), P0732 (gear 2), P0733 (gear 3), P0734 (gear 4), P0735 (gear 5), P076F (gear 7), P07D9 (gear 8) and P07F6 (gear 9). P0732 and P0733 run the same monitoring as P0731.

What symptoms does P0731 cause on the Cherokee?

You may notice any of these:

• A warning light, sometimes with a transmission message.
• Late or harsh engagement from a stop.
• Engine revs rising without matching road speed.
• The transmission limiting itself to certain gears or holding one gear.

What causes P0731 on the Cherokee, most likely first?

Here is how the usual suspects rank, most likely first.

How do you diagnose P0731 on a 2014-2018 Cherokee?

You will need a scan tool that reads engine and transmission codes and data, the wiring schematics for the transmission circuits, and basic hand tools.

What if the obvious fix does not work?

If the fluid level is right, the software is current and the speed sensors and wiring are sound, but P0731 keeps coming back, the problem is inside the transmission. The next suspects are the valve body (sticking valves or solenoids), then clutch C, and the TCM last, once everything else is ruled out. With the transmission open, inspect every clutch that applies in first gear, not just clutch C.

The common mistake is replacing a sensor or part on the code alone, before checking fluid condition, level and the stored data. What tends to work is correcting the level with the specified fluid, a software update followed by a relearn, replacing a valve body that is confirmed bad, and repairing wiring and connectors.

Your stop point is this: when the code returns with the fluid level right, the software current and the speed sensors and wiring sound, stop testing from outside and inspect the clutches, valve body solenoids and valves with the transmission opened.

How do you confirm the repair?

After any repair, reconnect anything you disconnected, erase the ABS, PCM and TCM codes, apply the parking brake, and warm the transmission above 43 C (110 F). If you repaired or replaced internal parts, check the fluid level and adjust it.

These relearns are required:

• If you replaced the TCM, the valve body, or a transmission that came without a TCM, run a valve body solenoid learn with the scan tool.
• If you did internal repairs or replaced the TCM, run a TCM adaptation.
• A TCM flash zeroes the adaptation cells, so a flash needs the relearn too.
• Skip the valve body solenoid learn on a car that only had its transmission assembly replaced, because it erases factory settings.

Then road test with fifteen to twenty upshifts so every gear gets used, from a standing start to 72 km/h (45 mph) with a steady throttle opening of 20 to 25 degrees. Below 40 km/h (25 mph), make five to eight wide open throttle kickdowns to first gear, with at least 5 seconds in second and in third between kickdowns. Read the codes afterward. If none set, you are done; if one sets, work that code.