Nissan RE4F04A / RE4F04B Problems: No 3rd After Kickdown, Harsh 1-2 Shift and P0720 - Diagnosis and the Real Fix

Nissan RE4F04A / RE4F04B Problems: No 3rd After Kickdown, Harsh 1-2 Shift and P0720 - Diagnosis and the Real Fix

Nissan RE4F04A / RE4F04B Problems: No 3rd After Kickdown, Harsh 1-2 Shift and P0720 - Diagnosis and the Real Fix

The Jatco-built RE4F04A and RE4F04B four-speed transaxle sat under Nissan, Infiniti and Mercury front-drive vehicles for well over a decade, and the failure pattern is remarkably consistent. The car drives fine until you ask it for a passing gear. You get a 4-2 or 3-2 kickdown, the engine flares, and third gear never comes back. Or the shifts go soft, the 1-2 is rough when cold, and eventually a shift takes so long the engine hits the rev limiter before the clutch grabs.

Owners usually hear "you need a transmission." Sometimes that is true. Very often the actual defect is a seal the size of a wedding ring, a valve body circuit, or a wiring connector a previous shop plugged into the wrong sensor. Here is how to tell those apart before you spend the money.

First: figure out whether you have an A or a B

These two units look the same and are not interchangeable. Sonnax's identification guide says the fastest field check on any 2000-and-later vehicle is the length of the valve body wiring harness: the RE4F04A uses a long wiring harness, and the RE4F04B uses a short one. Sonnax lists its remanufactured valve bodies for these units under separate part numbers - NIS137 for the RE4F04A and NIS136 for the RE4F04B - specifically because they do not cross over (Sonnax, Jatco/Nissan RE4F04A/B Valve Body Identification).

TransGo's published fitment gives a second cross-check. The RE4F04A side covers Altima 1993-99, Maxima 1992-99 plus the 2004 SL, Quest 1993-2002 plus 2004 S and SL and 2005-06 S, Infiniti i30 1995-99, and Mercury Villager 1993-2002. The RE4F04B side covers Altima 2000-06, Maxima 2000-03, and Sentra SE-R 2.5L 2000-06 (TransGo RE4F04A-HD2; TransGo SK RE4F04B). Note the overlap - a 2004 Altima and a 2004 Quest are not the same unit. Confirm by harness, not by model year alone.

Step 1: read the speed sensor codes correctly

This is the single most expensive mistake made on this transaxle, and ATSG's Wayne Colonna documented it in detail. A no-upshift complaint with a stored P0720 refers to the three-wire Hall-effect revolution sensor (output speed) that feeds the TCM directly. P0500 is a different sensor entirely - a two-wire AC-voltage speed sensor over the axle that reports to the combination meter first, which then puts the signal on the network for the ECM. Colonna describes shops replacing the two-wire sensor, then the instrument cluster, then the ECM, chasing a P0720 that was never about that circuit (Transmission Digest, "Getting Up to Speed with the RE4F04B").

Checking the sensor is easy: one wire is power, one is ground, and the center wire produces a 0-5 volt pulse to the TCM. Back-probe the center wire with the wheels turning on a lift. But here is the trap - if the transmission was recently out of the car, check that the revolution sensor and turbine sensor connectors are not swapped. They sit next to each other and use the same connector configuration, so the signal looks perfect at the sensor and never reaches the TCM because it is landing on the turbine speed input instead. Colonna notes why the swap does not announce itself: the turbine sensor reads the forward drum, held stationary in first gear, so there is no signal until the unit shifts to second. Per the same article, the revolution sensor harness is identified with white. Swapping the connectors back is the entire repair.

Related: a continuous P0717 turbine speed code after a rebuild usually means the wrong forward clutch drum went in. The low/reverse clutch lugs on that drum are what excite the turbine sensor, and per Colonna those lugs are shallower on the A version and taller on the B version. Put an A-style drum in a B unit and the air gap is too large to generate a signal.

Step 2: check the solenoid circuit before you condemn a solenoid

Sonnax publishes the connector pin-out and resistance values for the RE4F04A, which lets you check the whole pack from the case connector in a few minutes (Sonnax, RE4F04A Solenoid Identification & Connector Pin Out):

  • Pin 1 - Shift solenoid B: 20-40 ohms
  • Pin 2 - Shift solenoid A: 20-40 ohms
  • Pin 3 - Overrun solenoid: 20-40 ohms
  • Pin 4 - EPC (line pressure) solenoid: 2-5 ohms
  • Pin 5 - TCC solenoid: 10-20 ohms
  • Pins 6 and 7 - transmission oil temperature sensor
  • Pin 8 - empty

An out-of-range reading points at the solenoid or its harness. An in-range reading with a live shift complaint points at the valve body, not the electrical side. If you do need the pack, a matched RE4F04B shift solenoid kit for 2000-2006 replaces the whole set at once rather than leaving mismatched-age solenoids in a common circuit; the full range is in our transmission solenoid collection.

Step 3: check both grounds

Two ground wires run down to this transmission, and the small secondary one gets left unplugged after service. Colonna's article ties intermittent solenoid electrical codes to that small ground being disconnected together with a dirty main ground - cleaning the main ground and reconnecting the small one resolved the cases he handled. It costs nothing and belongs ahead of any teardown.

Step 4: separate a hydraulic problem from a pump problem

If pressure will not build at all, cooler flow tells you where you are. Sonnax's SonnaFlow chart for the RE4F04A describes the failed pattern plainly: poor pump output where line pressure and cooler flow cannot be maintained, with the correction listed as rebuilding the pump (Sonnax, SonnaFlow Chart: RE4F04A Nissan (Poor)). Normal flow with one specific missing gear is a clutch or circuit problem - and those are the ones worth repairing.

What actually fails: the direct clutch inner seal

TransGo's own correction list for this family names the root cause of the classic complaint. The RE4F04A kit is documented to correct "falling out of gear at a stop sign," "no 3rd after a 3-2 or 4-2 kickdown," "4-3 or 4-2 kickdown runaway," burned 3-4 clutches, and a leaking, worn, bad-design direct clutch (3rd) inner seal that "wears flat or opens up," along with soft 1-2 and 2-3 shifts (TransGo SK RE4F04A). The RE4F04B list is nearly identical and adds rough 1-2 when cold, hard or soft 1-2, and long shifts that hit the rev limiter, with the same upgraded direct clutch seal included in the kit.

In plain terms: the third-gear clutch loses its ability to hold pressure. On a kickdown the clutch releases, and when the unit tries to reapply it there is nowhere for pressure to build, so third never returns. Keep driving on it and the 3-4 clutches cook, which converts a seal-and-valve-body job into a full rebuild.

RE4F04B master transmission rebuild kit with frictions, steels, seals and gaskets
RE4F04B Master Transmission Rebuild Kit - frictions, steels, seals and gaskets in one box for a complete overhaul.

The fix

If the clutches still measure within spec and the unit has good flow, the repair is the valve body circuit plus the direct clutch seal - a job that stays on the bench and out of the teardown budget. If the 3-4 clutches are already burned, or the car has been driven for months with a flare, do it once and do it properly with a master overhaul kit that carries frictions, steels, seals and gaskets together. Our full transmission rebuild kit collection covers both the A and B variants.

Replace while you are in there

Cost and effort

Valve body work with the pan down is a half-day job for a competent DIYer with a torque wrench and a clean bench. A full overhaul means pulling the transaxle - realistically 8 to 12 hours of labor on most of these front-drive applications, plus rebuild time and a converter decision. Which of those two you end up paying for is decided almost entirely by how long the car is driven with a flaring shift.

FAQ

Can I put a firmer pilot valve spring in an RE4F04B to firm up the shifts? No. Colonna's article is explicit that this common RE4F04A trick backfires on the B unit because the TCC control valve is configured differently. Raising pilot pressure floods the TCC solenoid, which strokes the lockup control valve and applies the converter clutch - the car engages fine and then stalls as soon as you touch the throttle.

Will an RE4F04A valve body fit my RE4F04B? No. Sonnax carries them under separate part numbers and instructs you to check harness length before ordering precisely because they are not interchangeable.

My scan tool shows P0720 - is my transmission bad? Not necessarily, especially if the unit was recently removed and reinstalled. Check the revolution sensor signal at the TCM, not just at the sensor, and confirm the revolution and turbine sensor connectors are not crossed.

Working on a different Nissan unit? See our writeup on RE5R05A failures and coolant in the fluid.

Sources