How To Fix a Faulty Engine Control Module

A vehicle cannot operate safely without a working engine control module. Some manufacturers refer to an ECM as an engine control unit or ECU. Find out more about what this on-board computer does, and which vehicles are most likely to rely on an ECM. It can also be helpful to recognize the most common indicators of a faulty ECM and to keep a few key pointers in mind when attempting to reflash or replace this critical component.

What Does an ECM Do?

An ECM interprets data from sensors and adjusts electronic systems to improve engine performance. These systems control essential functions such as setting camshaft and throttle positions and managing ignition, fuel injection and variable valve timing. An ECM also plays an important part in controlling emissions as well as features such as turbocharger boost.

The earliest engine control module was the Computer Command System released by General Motors in 1979 for engines with carburetors or throttle body fuel injection systems. The CCS detected and read signals about engine speed, temperature and manifold vacuum and controlled fuel injection. Over the next two decades, ECMs made by General Motors and other manufacturers came to control more engine processes in conjunction with transmission control modules. Vehicles manufactured after 1996 may rely on an integrated powertrain control module or PCM to do the work of both an ECM and TCM.

How To Diagnose Engine Control Module Failure

A vehicle that has a faulty ECM may have several signs of failure. Malfunction indicator lights may randomly illuminate or the engine may not start at all if the module has failed. The clearest indication of problems with an ECM may be a check engine light that goes on and off without indicating the presence of mechanical problems.  If performance problems are present, it is a good idea to rule out mechanical causes before considering the ECM.

A vehicle may or may not operate as intended by the manufacturer if the ECM cannot receive accurate readings from sensors and interpret this data. An engine may choke, cough, sputter or stall if it does not receive enough fuel. Engines with too much fuel may have a reduction in fuel economy and increase in emissions. Engine control module failure can also prevent ignition, even though the engine may still crank.

What Is the TCM?

The transmission control module in a vehicle with an automatic or dual clutch manual transmission monitors sensors that indicate a need to shift gears. This system works along with the ECM to improve the functionality of the throttle as well as the cruise control and traction control systems. When a TCM is working properly, this system can help to reduce gear hunting and excessive wheel spin.

A TCM malfunction can also cause the check engine indicator to illuminate. Other issues that are more obvious when driving include delayed or unpredictable shifting. A vehicle that experiences difficulty shifting into higher gears and downshifting or that ends up getting stuck in the same gear may have a TCM problem. Vehicles with a traditional manual transmission do not have TCMs, and any electronic functions are performed by an engine control module or powertrain control module on newer vehicles.

How To Distinguish ECM and TCM Problems

While both ECM and TCM malfunctions can both cause the check engine light to appear. In general, major ECM problems may prevent a vehicle from starting or result in choking, backfiring or other engine-related issues. A malfunctioning TCM is more likely to cause problems when shifting gears. As these systems work together, it is possible that failure in one system could skew sensor readings for the other.

Error codes may also indicate incorrect sensor readings that involve the ECM or TCM. Error codes in the range of P0201 to P0208, P0301 to P0308 or P0400 to P0405 may point toward engine control module issues. A variety of other diagnostic codes such as P0480, and codes such as P0487, P0488, P0489, P0508, P0509, P060, P0622 and P1765 may also indicate issues involving the ECM or systems regulated by this component.

Some error codes that could be set by a malfunctioning TCM include P1765, P0751 or P0753. While it may be possible to distinguish between generalized engine and transmission problems based on how a vehicle operates, diagnostic testing is necessary to determine whether the ECM or TCM is at fault in a vehicle that relies on separate systems.

ECM Repair and Replacement

A vehicle with a faulty ECM should not be operated until this important component has been fixed or replaced. Depending on the system, the engine may operate in limp mode to make it possible to get a vehicle off of the road. Although a faulty ECM can cause malfunction lights to randomly turn on, it is advisable not to operate a vehicle with a flashing check engine light.

There are several approaches to repairing a functional engine control module. This component may need to be reflashed with updated software from the manufacturer in order to resolve persistent issues such as emissions issues, faulty error codes, hard starts, hesitation, poor fuel economy or rough idling. Reprogramming can often take place without the need to remove this component.

It is necessary to replace a failed ECM, and on-board computers can be costly parts. Replacement ECMs tend to cost less than PCMs, as these parts are typically found on older vehicle makes and models. The easiest way to replace an ECM is to use a pre-programmed part for a particular vehicle make and model that is loaded with the most recent manufacturer software. Otherwise, ordering a vehicle-specific ECM can cut part costs ahead of installation and programming.

It is crucial that the engine control module or ECU in a vehicle meets manufacturer specifications for engine operation. If this on-board computer cannot receive or process sensor readings, engine problems are likely to result. After ruling out mechanical causes, diagnostic testing can determine whether an ECM should be reflashed or replaced. Importapart ships replacement ECMs for any vehicle make and model within one business day of ordering.