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P0700: Transmission Control System Malfunction

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What is P0700?

Fault code P0700 is an OBD2 scanner Diagnostic Trouble Code (DTC P0700) defined as a “Transmission Control System Malfunction.”

The trouble code is triggered when your Transmission Control Module (TCM) detects a malfunction with the automatic transmission controls. This will send a Malfunction Indicator Lamp request (MIL request) and your check engine light will come on.

Whether you have a BMW or a Chevrolet truck, a TCM is vital for any automatic transmission. Your TCM monitors the sensors and actuators (throttle position sensor, motor speed sensor, and output shaft speed sensor) relating to your automatic transmission. 

It constantly communicates with your Engine Control Module (ECM) and Powertrain Control Module (PCM) to shift gears when necessary. When the control modules detect something wrong with your transmission, they trigger code P0700.

Note: DTC P0700 is simply informative. A more detailed diagnosis of the transmission control system is required to determine the real failure.

Common symptoms

Here are some common symptoms you may experience with an active P0700 engine code:

  • Illuminated check engine light (MIL illumination)
  • Transmission shifting problems
  • Failsafe mode
  • Engine stalling
  • A drop in gas mileage or fuel economy

Note: Failsafe mode (limp mode) is a feature in modern cars triggered when your ECM detects a problem. When the limp mode is active, your ECM restricts your vehicle’s drivability and speed — allowing you to “limp” to your nearest repair shop in a single gear and prevent damaging your vehicle further.

Can I still drive?

The P0700 error code could indicate drivability issues and a serious transmission problem either now or in the future, so discontinue driving immediately.

Driving with an active P0700 code can cause transmission shifting problems. You don’t want to be stuck in 4th gear when you’re meant to be in 2nd gear. You also run the risk of damaging your transmission system even more.

P0700 causes

There are multiple common causes for fault code P0700 and a transmission control system malfunction. These could be:

  • Low or dirty transmission fluid
  • Faulty TCM connectors or faulty wiring
  • A dirty or fouled TCM
  • Defective shift solenoids
  • A slipping converter clutch
  • A bad engine coolant sensor
  • A defective valve body

Diagnosis

Mechanics generally begin looking for cheap and easy-to-fix problems before moving on to more complex repairs.

  • First, your mechanic will use an OBD2 scanner to check your freeze frame data for other TCM codes.
  • Secondly, your mechanic will inspect your fluid levels to ensure your transmission fluid is clean and topped up.
  • Next, your mechanic will check your transmission module for faulty wiring and use a multimeter to test all the connection points between the Transmission Control Module, Engine Control Module, and Powertrain Control Module.
  • Next, they’ll use a scan tool and go on a test drive to compare the revolutions per minute speed of your torque converter with the revolutions per minute speed of your input shaft. This tests for a slipping transmission.
  • Finally, your mechanic will check your slip speed. If your slip speed is above 50 RPM, you have a slipping converter clutch.

When diagnosing a P0700 trouble code, the most common mistake is misidentifying the problem. Misidentifying it as a mechanical transmission fault or engine misfire rather than a TCM malfunction or sensor error could lead to needless repair costs.

Transmission repairs are expensive, so ensure your mechanic uses an OBD II sensor or scan tool to check for other TCM codes and a faulty Transmission Control Module.

Another common mistake is failing to thoroughly check the wiring harness. This can result in replacing a perfectly good TCM while leaving the underlying issue unaddressed.

If it’s a TCM problem, it’s easily fixed. If it’s a transmission problem, at least you know that before paying for a new transmission system.

Possible repairs for P0700 & Costs

Here’s how a mechanic fixes the P0700 trouble code:

  • Your mechanic will fix other check engine codes, which may cause P0700 to go away.
  • They’ll top off or replace your vehicle’s transmission fluid levels.
  • Your mechanic will replace all wires and connectors between your TCM, ECM, and PCM.
  • They’ll try to repair your TCM.
  • If a faulty TCM can’t be repaired, they’ll replace it.
  • If all else fails, your mechanic will replace your transmission.

The cost of fixing the P0700 error code and a transmission fault depends on the underlying issue.

Here’s how much repair costs will set you back:

  • Transmission fluid change: $80-$250 
  • Transmission fluid flush: $165-$290
  • Shift solenoid replacement: $150-$400
  • TCM repair: Around $300
  • TCM replacement: $500-$900
  • New transmission: $2,300-$4,400

Note: The repair costs above include labor charges.

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