P0702 – Transmission control system -electrical

By Benjamin Jerew (Contact Me)
Last Updated 2015-11-27
ASE Master Tech

Trouble CodeFault LocationProbable Cause
P0702 Transmission control system -electrical Wiring, ECM/PCM!TCM

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What Does Code P0702 Mean?

If you think about it, the modern automatic transmission does everything that a manual transmission does, modulating throttle position, clutch position, and gear position, all on its own, and the brains of the operation is the TCM (transmission control module). The TCM uses a number of actuators, such as solenoids and pressure regulators, to shift into different gears, depending on vehicle speed and driver demand.

The TCM also uses feedback from a number of sensors to verify proper operation. If a fault is detected, such as shaft revolutions out of range for a specific gear position, a DTC (diagnostic trouble code) will be set in memory. The ECM (engine control module), which is in constant communication with the TCM, will also set a DTC, referencing the TCM, and illuminate the MIL or CEL (malfunction indicator lamp or check engine light).

DTC P0702 refers to a general transmission control system electrical fault, but not to a specific fault, such as a solenoid open circuit, for example. On finding DTC P0702 stored in ECM memory, further diagnosis will be required to determine the nature of the fault.

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What are the common causes of code P0702 ?

Depending on year, make, and model, DTC P0702 may have number of causes. Here are some of the most common.

  • Wiring and Connectors – Damage and corrosion are typical for basic electrical failures of any kind, including TCM and ECM communication. Broken connectors or bad weather seals can easily lead to corrosion and water entry, leading to excessive resistance or short circuits.
  • TCM Failure – Barring external electrical faults, the only thing left would be internal faults, such as a shorted internal voltage regulator or open transistor. Manufacturing faults are rare, but not unheard of, and impact damage can easily lead to this type of failure.

What are the symptoms of code P0702 ?

Depending on the vehicle, the driver may or may not notice any drivability problems associated with the illumination of the MIL. Depending on the vehicle’s limp-home mode conditions, automatic transmission function may continue more or less as normal.

On the other hand, less hydraulic-dependent automatic transmissions may drop gears, such as being unable to shift out of 1st and Reverse, or the vehicle may only run in 2nd or 3rd gear. Some vehicles may exhibit difficulty starting, rough idle quality, or stalling when coming to a stop.

No matter what the symptoms, an illuminated MIL indicates that the vehicle is running in a non-efficient limp-home mode, sacrificing fuel economy and comfort for the most basic automatic transmission and engine functions. Immediate diagnosis and repair is recommended.

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How do you troubleshoot code P0702 ?

DTC P0702 is typically linked to an electrical fault, which may be internal or external to the TCM. After making sure that all modules have proper power and ground, check the following:

  • If the TCM is separate from the ECM
    • Check the wiring harness between the ECM and TCM, looking for damage, which could cause an open circuit or short circuit and communication failure. Crushed wires, rodent damage, or road debris damage are common.
    • Check the connectors at the ECM and TCM, looking for bent pins, water entry, or corrosion, any of which can cause signal failure.
    • With no electrical problems noted, internal TCM failure could be the cause of the problem. A reflash may be applicable, or replacement of the unit may be required.
  • If the TCM is part of the ECM, then an electrical failure is basically a module failure. Look for broken or bent pins, water entry, or corrosion, which could cause this problem. Otherwise, a reflash may be available or you will have to replace the entire module.

 

Codes Related to P0702

If DTC P0702 is present in ECM memory, look for other TCM-related codes to aid in your diagnosis. These may include:

  • P0613 TCM Processor
  • P0614 ECM/TCM Incompatible
  • P0706 Transmission Range Sensor Circuit Range/Performance
  • U0101 Lost Communication With Transmission Control Module

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