Troubleshooting Infiniti Transmission Problems

Infiniti transmission problems can be caused due to something as simple as a low transmission fluid level. Erratic or no shifting can indicate a more serious problem, such as a faulty valve body and a bad torque converter. Troubleshooting Infiniti transmission problems requires a diagnostic scanner that can read transmission fault codes.

This guide will tackle common problems and steps to help you troubleshoot Infiniti transmission problems, such as limp mode, no shifting, delayed shifting, and slipping.

Common Infiniti Transmission Problems

Common problems that often cause Infiniti transmission problems:

• Low transmission fluid level – Low transmission fluid level can cause many issues, including erratic shifting, no shifting at all, delayed shifting, strange grinding noises, limp mode, and even check engine light to come on.
• Faulty Torque Converter – This can cause MAKE transmission to slip in all gears, shudder, and even overheat.
• Worn Transmission Bands –  Can cause delayed shifting, shifting at high RPM, harsh shifting, no gear at all, and no reverse.
• Faulty Shifter Module – A faulty shifter module or shifter cable can cause the transmission to get stuck or not go in the selected gear.
• Defective Valve Body – The valve body is complex and can fail in several ways. Depending on the competent that fails, it can cause limp mode. The transmission may not shift at all or harsh shifts between gears or specific gears. It does not apply to the CVT transmission.
• Faulty Vehicle Speed Sensor  – If your Infiniti has developed a harsh shift or is stuck in emergency mode (limp mode), the vehicle speed sensor (VSS) may be the problem. Sigal from the VSS is sent to the Powertrain Control Module (PCM), and the last signal can cause one or more of the previous systems.
• Brake Light Switch – A faulty brake light switch can prevent the shifter from moving out or back in Park.
• Low Battery Voltage – In some cases, the low voltage can trigger Infiniti’s automatic transmission to get stuck in limp mode.
• PCM / TCU / ECU Software Issue – Software issues can cause erratic shifting or downshifting issues. Infiniti transmission may shift too late or cause gears to drop unexpectedly.  Infiniti dealers may have a software update to fix such shifting problems.
• Wire harness – Damages of wire harnesses from ECU / PCM to the transmission housing can cause shifting problems. For example, your Infiniti may not shift or go in gear.

Troubleshooting Infiniti Transmission Problems

Limp-home mode

Older Infiniti vehicles with 4-speed automatic (RE4F04B) transmission suffer from issues stuck in limp-home mode. The transmission gets stuck in 2nd or 3rd gear and will no longer change gears. This may happen immediately after starting the car or while driving. The check engine light will be illuminated.

Possible causes and solutions:

• Faulty speed sensors give false and implausible data to the TCU. There are two-speed sensors, input and output, at the side of the gearbox. As a preventive measure, the TCU activates the limp-home mode and stores a P0720 code.
• Misconnected speed sensors. Suppose this happened after the car underwent some repair. In that case, it is possible that someone disconnected speed sensors for some reason and then reconnected them incorrectly, as they both have identical connectors. This is a common mistake that happens during various repairs.

Harsh or delayed gear shift

Front-wheel drives Infiniti vehicles with 5-speed automatic (AW55-51SN) transmission can suffer from harsh and delayed gear shifts between all gears. The car will usually run fine while cold, as this problem will appear after warming up. This issue comes with an illuminated check engine light and corresponding code in the fault memory.

Possible causes and solutions:

• Faulty pressure solenoid, which gets stuck in a wide-open position. As a result, transmission fluid pressure is not controlled, which gets too high. This causes harsh gear shifts and triggers a check engine light, with a P0797 code being stored in the DTC memory. Changing the affected solenoid will solve this issue. There are various remanufactured kits available.
• Dirty and degraded transmission fluid can cause shift issues, as the sludge obstructs solenoid movement. Although transmission fluid flush filter renewal can help, sometimes the solenoids will be damaged beyond recovery, and replacing them is the only option.

Erratic and failed gear shift

Rear-wheel drive Infiniti vehicles with 5-speed automatic (RE5R05A) transmission can have various shift issues, ranging from harsh and erratic shifts to failure to engage certain gears. This problem may be constant or intermittent, but it will usually trigger a check engine light.

Possible causes and solutions:

• Failed solenoid valve, either one that controls the direct clutch, front brake, or input clutch, depending on the stored code.
• Damaged or corroded wiring causes interferences in communication between the TCU and solenoids. As the symptoms will be identical to those of a failed solenoid, checking both wiring and solenoid before replacing is recommended.
• Broken or corroded connectors on the control board cause intermittent loss of communication. Cleaning out any traces of corrosion usually helps. However, instead of soldering broken connectors, it is better to replace the control board.
• Some of these problems can result from transmission cooler failure, as it causes the mixing of coolant with transmission fluid. If not flushed thoroughly, this contamination will cause various damage to solenoids, wirings, and connectors.

Shudder while engaging higher gears.

Rear-wheel drive Infiniti vehicles with 5-speed automatic (RE5R05A) transmission can develop a noticeable shudder when engaging 4th or 5th gear, causing harsh and bumpy gear change. This will not happen during the 1st-3th gear shift; in most cases, it will not trigger a check engine light. The problem is usually more prominent when the vehicle warms up.

Possible causes and solutions:

• A worn TCC (torque converter clutch) control sleeve causes a loss of pressure inside the valve body. This results in harsh or failed clutch engagement and can even lead to slippage within the torque converter. As this is a well-known issue, several upgraded control valve kits are available.

Harsh downshifts

Rear-wheel drive Infiniti vehicles with 7-speed automatic (JR710E or JR711E) transmission can display mild or severe harsh downshifts. This happens during shifts between any gear and doesn’t depend on the load or speed. The problem is intermittent and usually only when the vehicle is warmed up. It will not trigger a check engine light.

Possible causes and solutions:

• A worn sleeve for the Low brake switch causes pressure loss inside the valve body. The resulting inadequate operation of low brake assembly leads to harsh downshifts. As this is a well-known issue, several upgraded control valve kits are available.

Delayed gear shifts

Four-cylinder rear-wheel-drive Infiniti vehicles that use a 7-speed automatic (W7C700) transmission can develop sudden and intermittent symptoms, ranging from harsh and delayed gear shifts to gear slippage or going into limp-home mode. Thesesues will trigger a check engine light, so a corresponding error code will be stored.

Possible causes and solutions

• The faulty conductor plate holds the solenoids and connects them to the TCU. When the conductor plate is faulty, it causes communication problems, which results in improper solenoid operation. This is a well-known problem, and there are numerous aftermarket solutions.
• Worn or faulty valve body solenoid. Sometimes, the problem can be damage to the internal wiring.

How to Troubleshoot Infiniti Transmission Problems

Following the steps will help you troubleshoot and isolate Infiniti transmission problems.

Read Transmission Fault Codes

The YOUCANIC Full System Scanner can read and clear fault codes through every vehicle’s control module.

The first step is to read fault codes from the transmission control module, or what is known as the TCU. To read these codes, you will need an Infiniti Nissan Transmission Scanner. Generic OBD2 code readers are not recommended because they may not show a fault code even when there is a transmission problem.

1. Park the vehicle and turn off the ignition. Set parking brakes.
2. Locate the diagnostic port under the dashboard, driver’s side.
3. Plugin your OBD-II scanner, then turn on the ignition without starting the engine. 
4. The scanner will turn on. Allow it to communicate with the vehicle. Select Infiniti, then the particular models. For example, G35. 
5. Select Control Units, then Transmission.
6. Select Read Fault Codes from the main menu.

The fault codes you will get with a transmission OBD2 scanner can be beneficial compared to a generic OBD2 scanner.

Reset Transmission Adaptation

If you have a newer Infiniti, resetting the transmission shift points to the factory setting. The best way to reset the Infiniti transmission is to use a diagnostic scanner to reset the Engine Control Unit and Transmission Module.

If a diagnostic scanner is unavailable, an ECU reset can be done by disconnecting the battery and leaving the lights on (even though they won’t turn on because there is no power) to release any residual capacitive voltage. Wait a half hour before you reconnect the battery.

This simple procedure can improve shifting, does not require any tools, and does not cause adverse effects. You will have to synchronize windows and store radio stations.

 Check Infiniti Transmission Fluid Level

If your Infiniti transmission is not shifting properly, shifting late, or slips, you must first check the transmission fluid level. Checking the transmission fluid level is easy if your Infiniti has a transmission dipstick.

1. Park the vehicle on level ground when possible.
2. Set the parking brakes and shifter in Park.
3. Pull the hood release and open the hood.
4. Locate the transmission dipstick.
5. Remove the dipstick and clean it with a clean cloth.
6. Reinsert the dipstick in the transmission. Ensure the transmission is fully inserted, then remove it.
7. Look carefully at the dipstick to determine the current transmission fluid level. The level should be between MIN and MAX for the COLD (lower) markings.
8. If the level is low, add a transmission fluid level.
9. Drive the vehicle for 15 minutes and select all the gears manually.
10. Repeat the procedure once the transmission warm-up, but this time, the level must be between the MIN and MAX marks for the HOD (higher) markings.

Not all Infiniti vehicles have a transmission dipstick. If the dipstick is absent, the vehicle must be raised on a lift, and the level can be checked via the fill hole.

Check For Recalls

Lastly, check if any open recalls or Technical Service Bulletin (TSB) exist for your Infiniti that apply to the transmission. If they exist, recalls are performed free of charge by any Infiniti dealer. Visit our Check Recalls page to check if a recall exists on your vehicle.

Ask the nearest Infiniti dealer if there is an update for transmission. Infiniti Technical Service Bulletins (TSB) typically update the transmission’s engine or Transmission control unit software. TSBs typically program the shift solenoids, shifting the transmission quickly or later depending on the issue.

We hope you find the Troubleshooting Infiniti Transmission Problems guide helpful. Check these troubleshooting and repair guides for more help on your Infiniti.