P0634 PCM/ECM/TCM Internal Temperature Too High

P0634 code definition

The P0634 code is triggered when a control module detects internal temperatures that greatly exceed the manufacturer's levels, and which are thought to be disastrous.

What the P0634 code means

A P0634 is an OBD-II generic code that appears when a control module in the vehicle detects a temperature reading at some point in the entire system that is going to lead to a major malfunction or breakdown. All of a vehicle's control modules have self-preservation levels and self-testing modes to prevent disaster, and this code can be triggered by any of them.

What causes the P0634 code?

A P0634 is caused only by a few issue:

• A faulty control module
• A short in the wire

What are the symptoms of the P0634 code?

The symptoms associated with the P0634 code vary widely and range from the service engine light coming on to something as serious as a no-start condition or engine stall. Because the issues that would cause a module to set this code are catastrophic, if there is no problem with the vehicle, it typically means that the module has failed, which is an unusual event.

How does a mechanic diagnose the P0634 code?

To diagnose P0634, the mechanic needs an OBD-II scanner and they will use the freeze frame data to understand when the code appeared and if there are any other associated codes. They will reset the fault codes and test the vehicle to determine if the code reappears. If it does, they will test the power and ground circuits on the module identified by the scanning and diagnostics. If the levels are not in line with the manufacturer's settings, they will make repairs or decide if the module needs to be replaced.

Common mistakes when diagnosing the P0634 code

Quite often, this code can be due to shorted wiring in a module, yet technicians may mistakenly believe that more than a single control module is to blame for the code. Diagnosis with a CAN Bus scanner or an Autohex is one of the better ways to narrow down the field and understand the source of the issue.

How serious is the P0634 code?

This is a very serious code because it usually means that a control module has suffered a fatal issue or that a serious electrical problem caused it to malfunction and cease to perform its programming. This can leave the vehicle in a no-start condition.

What repairs can fix the P0634 code?

To repair the P0634 code, a mechanic should:

• Use the scanner to verify the code, documenting any other codes that appear and using freeze frame to gauge the order in which codes occur.
• A visual assessment of the wiring and connectors of the control module identified will be done, and any repairs needed will occur. This may mean replacing or repairing fuses, components, wires or connectors that are damaged, disconnected, shorted or corroded.
• The control modules power and ground circuits must then be tested and compared against the manufacturer specs. This may lead to further repairs or component replacement.
• A final test with the scanner is done to determine if the issue is repaired or if a faulty control module has caused the problem.
• A new control module may be required.

Additional comments for consideration regarding the P0634 code

Should it be necessary to replace a control module, it is going to require that the device is reprogrammed to match the vehicle's settings. Control module failure is very rare, but when you have this code, it is quite likely that it is the module that has caused the problem. There are many modules that work with the powertrain control module or PCM as well as the engine control module or ECM and the transmission control module or TCM. It is important to take the time to determine the source of the code.

Need help with a P0634 code?

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