2006 Dodge Stratus P0128 Code: Causes, Symptoms, and Diagnostics After Thermostat Replacement

The P0128 code alone does not typically cause an engine to shut off. It's important to use a proper OBD2 scanner to check for additional fault codes. Do not rely on the 'key dance' trick as it is ineffective. Ensure you used the correct thermostat (195°F), and confirm that the cooling system was properly refilled with coolant and any air pockets were purged from the system. Also, verify the voltage output of the ECT sensor — check the tan/blk wire for proper signal (should be around 0.5V to 4.5V depending on temperature).

Yes, I've confirmed the serpentine belt is in good condition. I'm now considering whether a failing alternator could be contributing to the issue — especially since the car seems to struggle under load.

I’ve scanned the system multiple times, but no additional fault codes appear. The P0128 code is the only one present.

Are you using a full-function OBD2 scanner? It's unlikely that an alternator failure is the root cause — your symptoms suggest a thermostat or sensor issue rather than electrical system failure. This is fundamentally a thermostat rationality problem: the PCM is receiving inconsistent data from the coolant temperature sensor and thermostat, leading to incorrect engine warm-up timing. To diagnose properly, you must scan for additional codes and measure the voltage at the ECT sensor (tan/blk wire). Also check if any auxiliary systems are malfunctioning — such as the A/C or outside temperature gauge — which could cause confusion in interpreting symptoms.

All vehicle functions appear normal. The car seems to 'try' to start but fails to ignite fully, like it's struggling to turn over properly.

I did use a scanner initially, but I had to return it due to technical limitations — the device couldn't provide detailed diagnostics or real-time data.

Let's start with this: Does the engine crank when you turn the key? Is it spinning slowly (like a weak crank) or just making a single click? Is the security light (anti-theft) illuminated during startup?

When I turn the key, I hear a clicking sound — the engine attempts to turn over but doesn't fully engage.

I agree — 'tries to turn' suggests a possible battery issue. The engine seems to spin very slowly compared to normal startup behavior. If this is accurate, try giving the vehicle a jump start or using a battery charger. If it still doesn't start after a jump, then basic diagnostics are needed: check for spark at multiple plugs and verify fuel pressure. These are foundational checks in engine troubleshooting.

Yes — I gave the car a jump start. It attempts to catch fire but still fails to start fully.

There's no magic fix here — you'll need to perform comprehensive diagnostics. Check for spark, fuel pressure, and injector pulse. Without a full OBD2 scanner capable of real-time data capture, these tests are difficult but essential. These are fundamental auto diagnostic skills — they apply regardless of the P0128 code.

Thank you for the helpful guidance. I'll proceed with the recommended diagnostics step by step.