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P00B7 Chevy Cruze — diagnose and fix

Diagnose and fix a P00B7 Chevy Cruze trouble code

What is a P00B7 Chevy Cruze trouble code?

A P00B7 Chevy Cruze Engine Coolant Flow Insufficient trouble code can set when the ECM detects a temperature difference of more than 68°F between the radiator coolant temperature sensor (RCT) and the engine coolant temperature sensor (ECT). The ECM monitors both sensors to determine whether the electrically heated thermostat is allowing sufficient coolant flow to keep the engine at operating temperature.

What is an electric thermostat?

Car makers are installing smaller engines paired with a turbo

electric thermostat, PPPB7

Electric thermostat and housing used on small engines

to get the power of a larger engine, but with increased MPG. Because the engines are smaller, they may not generate the same amount of heat at idle as a larger or older engine. In addition, short trip driving and low heat generation by the engine may prevent the thermostat from opening as quickly. As a result, the engine doesn’t reach full operating temperature as quickly and may not provide enough passenger compartment heat.

Traditional wax pellet thermostats are slow to respond to temperature change in the engine coolant. So car makers added a heater to the wax pellet to force it to open faster to allow full coolant flow and prevent overheating.

The newer electric thermostats are designed to fix that problem. The wax in the pellet can be heated by the engine coolant OR, by applying a pulsed current to the heater located inside the pellet. The pulsed current is determined by the ECM.

When operating properly, the thermostat begins to open with by itself when engine coolant reaches 217°F. When 12V current is applied, the thermostat begins to open at 176°F. The thermostat should be fully open at 243°F. The ECM makes the determination whether pellet heating should be done by the engine coolant or by the heater, depending on load conditions

NOTE: GM recommends you DO NOT replace the engine coolant thermostat unless you find a thermostat related trouble code. The ECM monitors the thermostat every time you start the engine and compares the ECT readings to the RCT readings to ensure the thermostat is operating within design parameters.

IMPORTANT: These smaller engines may take longer to reach normal operating temperature. By itself, that is NOT a reason to replace the thermostat. If there are no thermostat related trouble codes and the engine coolant is at the proper level, do NOT replace the thermostat. Do not replace the thermostat as “routine” service when changing the engine coolant.

Symptoms of P00B7 Chevy Cruze trouble code

When a P00B7 Chevy Cruze trouble code sets, you may notice that the radiator fans are running at high speed at all times when the engine is running. This is due to the fact that the ECM has detected a large enough difference in temperature between the ECT and RCT to conclude that coolant flow is too low, so it switches the radiator fans to high to prevent engine overheating

Diagnose the P00B7 Chevy Cruze trouble code

  1. Check fuse F47 located in the underhood fuse box. This fuse supplies current to the thermostat heater.
Chevy cruze P00B7, thermostat

Electric thermostat fuse #47 in underhood fuse box Chevy Cruze

2. Check for battery voltage on the violet/dark blue wire at the thermostat heater.

3. Check the dark blue wire running back to the ECM. You’re looking for opens or short to ground

4. If you have a bi-directional scan tool, command the thermostat heater to run at 100%. Increase idle speed to 3,000RPM. That will cause the thermostat to open fully and you should see coolant temperature drop to less than 185°F.

5. If the temperature does not fall to less than 185°F, replace the thermostat

6. Clear the trouble code after the repair to shut off the high speed fans

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Posted on by Rick Muscoplat

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