P0702: Transmission Control System Electrical OBD-II Trouble Code

• How Serious is the Code?
• Symptoms
• Causes
• How to Diagnose the Code?
• Common Mistakes When Diagnosing
• What Repairs Will Fix P0702?
• Related Codes

If you are curious about the cause of a P0702 DTC (diagnostic trouble code) from your vehicle, the answer is very simple and very confusing depending on the vehicle’s drivability.

Need a replacement transmission? Get an estimate for replacement transmissions and local installation. Look up your transmission model by vehicle make and model.

What Transmission Do I Have?

The DTC P0702 – Transmission Control System – Electrical, simply means that something went wrong in the electrical system that controls the automatic transmission. It is a generic trouble code that every vehicle using OBD-II has in common.

There should always be another code stored in conjunction with P0702. That will be the key, solve that other problem and usually P0702 goes away.

The TCM monitors all of the actions electronically and mechanically of an automatic transmission. It analyzes several inputs from sensors, makes millisecond decisions, then controls several more outputs to hydraulic valves and solenoids and does all of this while keeping an eye on several more stats from the Engine Control Module (ECM).

How Serious is the P0702 Code?

The question is, how serious is the underlying condition that produced this code? The second code will provide more information on the cause of any problems. The second DTC can be from the TCM or ECM. If the vehicle is not experiencing any obvious drivability issues, the DTC may have been set from an anomaly or simply a discharged battery. If it is shifting hard or not at all, it may indicate catastrophic failure.

Taking note of any other symptoms will help with further diagnostics. Please note that if you have a manual transmission this code may not apply. It’s possible the vehicle had the ECM replaced and is using one that originally controlled an automatic transmission. Depending on make and model this may not even be possible.

Symptoms of P0702

Here are some common symptoms for P0702. Remember that your vehicle may experience some or none of these behaviors.

• Check Engine Light illuminated
• Traction Control Light illuminated
• Abnormal shifting – revving higher than normal before shifting
• Harsh shifting
• Delayed response when changing gears
• Stalling when slowing down
• Limp Home Mode – limits vehicle to one gear and speed limit in order to get the car to a garage (limp home)
• Fluid leak/burning smell from transmission area – usually red / brownish color or black if things got real bad

Causes of P0702

Depending on the make, model and year of vehicle the causes will vary. Manufacturers use unique electrical designs and engineering so a DTC can mean different things to different vehicles. These are some of the more common causes associated with P0702 being set.

• Open/Short in a wire
• Low Fluid
• Slipping transmission / spinning tires
• Sticking/defective solenoid or valve
• Recent battery discharge
• Torque converter problem
• Hydraulic system problem

How to Diagnose the P0702 Code?

To properly diagnose this code you will need a computer/scanner, a volt/ohm/amp meter (multi-meter) and probably a wiring schematic. The vehicle should first be road tested to verify concerns and gather data.

Some aftermarket code readers will only give generic codes and not sub group specific. You may have to take it to a licensed shop that has the proper equipment to read your vehicle’s subsystem codes.

First you can try clearing the code. Before you erase it, write down all present codes, snapshot any data is about to be cleared and any info from the first road test. If the codes will clear and not return during final road test, the code may have been set by an anomaly or glitch such as a sticky solenoid, valve or erratic sensor reading. Studying freeze frame data might provide insight to the conditions that set the code.

If the codes immediately return or come back consistently on road tests you will have to thoroughly inspect the affected circuit related to the DTC’s. This may require access to internal parts of the transmission as some solenoids and connectors will only be accessible with the transmission oil pan removed.

Common Mistakes When Diagnosing P0702

Under Diagnose

Don’t clear the code and assume because it doesn’t come right back that the vehicle is fixed. A small problem may become a big one.

Over Diagnose

Not getting all codes and data that set the P0702 code and recommending extensive repairs when a wire repair or sensor replacement would have fixed it.

What Repairs Will Fix the P0702 Code?

• Transmission Fluid fill or change
• Wire or Sensor replacement or repair
• Transmission overhaul/replacement

Codes Related to P0702

• P0603 TCM Processor
• P0614 ECM/TCM Incompatible
• P0705 Transmission Range Sensor Circuit
• U0101 Lost Communication with TCM

Links To Diagnostic Codes

Links To Symptoms

Comments

Have this code? Found a fix? Note it in the comments below.

Need a replacement transmission? Get an estimate for replacement transmissions and local installation. Look up your transmission model by vehicle make and model.

What Transmission Do I Have?