A failed PCM will definitively result in a no start condition, although you should not be quick to blame the PCM without first performing a series of basic diagnostics in order to narrow down the problem as PCM failures are not necessarily “common”. Most of the PCM failures we come across are the result of aftermarket devices such as performance tuners/programmers. Although unaware of the reasoning as to why these devices seem to stress the PCM, we’ve replaced many non-responsive or otherwise malfunctioning PCMs on vehicles equipped with such devices.
The number one symptom of a PCM failure is the inability to connect a scantool or diagnostic system to the PCM. Before replacing the PCM, we recommend verifying that the PCM relay and diode in the underhood fuse panel are in working condition. If one of these components fails, the PCM will fail to power on and the problem may be misdiagnosed. If replacing your PCM, also replace the PCM relay and diode. The locations of these components may vary and are identified in your owners manual.
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• Disconnect the negative battery terminal, then the positive battery terminal.
• Remove the battery from the vehicle.
• Remove the battery box/tray bolts with a 13 mm socket (4 bolts). If the bolts are corroded (as pictured), take necessary precautions to avoid coming in contact with caustic debris.
• The PCM travels through the firewall on the passenger side. The device itself is located inside the cabin, however the connector is only accessible from under the hood. Use a 10 mm socket to completely loosen the PCM connector retaining bolt, then carefully disconnect the connector from the PCM (note - the bolt will stay with the connector as it is loosened; do not attempt to remove it from the connector).
• The PCM is located under the dash behind the passenger side kick panel. With the panel removed, remove the small black plastic clip that secures the PCM to the mounting bracket.
• To remove the PCM from the mounting bracket, maneuver it towards the driver side slightly, then pull straight out.
• Reinstallation is exactly opposite removal; do not overtighten PCM connector retaining bolt.
• Locate and replace the PCM power relay. The location may vary by model year, refer to your vehicle's owners manual.