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Q: It starts when cold, once it warms up or hot outside it won't start

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I've replaced radiator, water pump & thermostat, still dies once warms up or if hot outside it won't start. Not sure where to start! Cat is hot but not so hot you can't touch. Pretty sure electrical.

My car has 235000 miles.
My car has an automatic transmission.

Hello. Thanks for writing in about your 1999 Jeep Grand Cherokee. From the symptoms you describe, it would not appear that the vehicle’s issue is with the cooling system. More likely than that, as you figured, it may be an issue that is electrical in nature.

A few things that can typically produce the symptoms you are experiencing are a faulty ignition module or starter. The ignition module is the electronic component that provides the vehicle with spark signal. Over time, the module can wear out due to exposure to engine heat. The module may function properly when it is cool, however, when the engine warms up the module it may cease to function. This will usually continue to occur until the component fails completely.

The starter is also susceptible to issues with heat. This may be another possibility if the engine is not cranking when it warms up. I would recommend looking into those components first, before moving on to other systems. If you need to have an expert take a look, a certified pro from YourMechanic can come to your car’s location to diagnose the hard starting issue and make the correct repairs.

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