Technical Description of OBD-II Trouble Code
Range/Performance Issue in the Transmission Control System
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to all vehicles manufactured from 1996 onwards (Ford, Honda, Mazda, Mercedes, VW, etc.). Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
If the malfunction indicator lamp (MIL) on your vehicle’s instrument panel is illuminated and accompanied by a stored code P0701, it means that the powertrain control module (PCM) has detected a malfunction in the transmission control system. This code is only relevant to vehicles equipped with an automatic transmission.
While most OBD-II equipped vehicles have integrated transmission controllers within the PCM, there are still some manufacturers that use a separate transmission control module (TCM). Regardless of the type of system, transmission-related codes are stored as P-codes (there are no T-codes). If the P0701 code is stored, it is highly likely that there are other transmission control codes stored as well.
Automatic transmissions in OBD-II equipped vehicles are controlled electronically. This involves a control module, a controller area network (CAN), various sensors and solenoids, a hydraulic pump, and a hydraulic valve body.
The transmission controller receives voltage signals from engine and transmission sensors. Engine sensor inputs include throttle angle, engine RPM, load percentage, and coolant temperature. Transmission sensor inputs monitor pump pressure, transmission input speed (RPM), transmission output speed (RPM), shifter position, vehicle speed, torque converter lock-up percentage, and transmission temperature, among others. The transmission controller uses these input signals to determine shift strategy and electronic pump pressure parameters. The electronic pressure control valve regulates pump pressure to ensure smooth shifting. Applying maximum pump pressure directly to the valve body would result in extremely harsh shifting and potential damage to driveline components. Electronically controlled solenoids operate spring-loaded ball valves to control high pressure fluid flow, enabling desired up and down shifts. Another solenoid controls the percentage of torque converter lock-up, improving fuel efficiency and power delivery to the wheels.
The CAN is a complex system of wiring and connectors used to transmit data between the TCM (if applicable) and the PCM. Data, including stored codes, may also be shared with other controllers via the CAN. Transmission input and output speed (RPM), vehicle speed, and transmission temperature are shared among various controllers. This data is used for comparison in anti-lock braking systems, electronic traction control systems, and electronic stability control systems, among others.
This code is unique in that it is usually only stored if other transmission-related codes are present. These codes may be related to mechanical or electrical issues.
Symptoms & Severity
If this code is stored, you may have noticed that your transmission shifts more harshly than usual. This is because the transmission control system has entered limp-in mode, where transmission pump pressure is significantly increased. Limp-in mode is not intended for long-term use. If your vehicle has displayed a code P0701, it should be diagnosed promptly.
Symptoms of a P0701 code may include:
Causes
Possible causes for this code to be set are:
Diagnostic and Repair Procedures
It is always a good idea to check for technical service bulletins (TSB) specific to your vehicle. Your issue may be a known problem with a known solution provided by the manufacturer, which can save you time and money during diagnosis.
To diagnose a P0701, you may need a scanner, a digital volt/ohmmeter, a transmission pressure gauge, and a vehicle service manual (or equivalent).
Start with a visual inspection of the transmission control wiring and connectors. Also, check the battery, battery cables, and battery terminal ends at this time.
Connect the scanner to the vehicle’s diagnostic connector and retrieve all stored codes and freeze frame data. Write down this information and keep it for later reference.
Since low fluid level and/or condition is the leading cause of transmission failure, check the fluid level now. Follow the manufacturer’s specifications for checking the transmission fluid level.
If the fluid has a strong burnt smell, it indicates catastrophic mechanical failure that will require a complete transmission rebuild and a new torque converter. If the fluid level is more than one quart low, refill the transmission with the recommended fluid and start the engine. Inspect the transmission, transmission cooler, and cooler hoses/lines for any leaks. Repair any leaks as necessary. After fixing the leaks and correcting the fluid level, test drive the vehicle to see if the code/s reset. If they do not, then the code was related to the low fluid condition and it has been resolved.
If the code/s immediately reset, refer back to the recorded freeze frame data. Begin by diagnosing the code that was stored first and diagnose/repair all other stored transmission control codes before attempting to diagnose the P0701.
Additional diagnostic notes:
