NP231 (Command-Trac) holds about 2.2 pints (~1 qt) of ATF. Mopar spec is ATF+4 today; Dexron is acceptable. Use 8mm hex drive for plugs.
The New Process 231J is the part-time transfer case in most XJs (NP242 Selec-Trac is the full-time option, see separate entry). Capacity is 1.0 L (2.2 pints, over 1 quart). Fluid is ATF - originally Dexron II, now ATF+4 per current Mopar TSB, though Dexron III/VI works fine and some owners run a synthetic ATF or 30W oil for marginally better cold shift effort. Drain and fill plugs are 8mm hex (5/16 Allen) and sit at 5 o'clock and 9 o'clock on the rear of the case. Fluid should reach the bottom of the fill hole. Check more often than the engine - the input shaft seal weeps onto the transmission tailshaft and the rear output seal drips onto the rear driveshaft, both common XJ leaks. A black ring around the speedo sensor on the tailhousing is also a known leak point - replace the o-ring (Mopar 83503064).
| Part | Vendor | Est. price |
|---|---|---|
| ATF+4 (1 qt) | any | ~$10 |
| Speedo sensor o-ring | Mopar | ~$2 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.