Question about BMW 325

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I have a 2006 bmw 325i 3.0L E90. Car has been overheating and got a code of P0597 Thermostat Heater control circuit open. I replaced the thermostat with a new aluminum Wahler unit. Just drovve it for 10 miles and it overheated again. The fat hose going into the thermostat is a lot cooler than the other hoses, so it looks like it's still not getting a signal to open the thermostat when it get warmed up. Anybody have a solution?

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IT sounds like heater control valve not thermostat. Check Pelican or for tech advise & tips. Also check (enter your cars specs and you will see exploded diagrams)

Posted on Apr 04, 2011


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Engine trouble codes

Hi CJ-
For many years now, engine codes have been standardized throughout the automotive industry to ease in vehicle diagnostics-so these codes are the same regardless of the maker of your car.
I use a site "", to look these up on line. This is an excellent site since it not explains the code, but also troubleshooting methods for mechanics to fix the problem. For ease of information, I have provided the links for the codes you listed.
It sounds as though you may have issues with your O2 (oxygen sensor) which monitors the combustion and emissions system in your car.
Though rates vary from shop to shop, this should not be a wallet busting repair if replacement is needed.
P0597 MINI Thermostat Heater Control Circuit Open P0036 HO2S Heater Control Circuit Bank 1 Sensor 2 P0037 HO2S Heater Control Circuit Low Bank 1 Sensor 2

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P0597 code

P0597 Thermostat Heater Control Circuit/Open

Circuit/System Description

The engine control module (ECM) controls the pulse width modulated (PWM) thermostat. The thermostat controls coolant flow and regulates the engine operating temperature. Ignition voltage is supplied directly to the thermostat. The ECM controls the thermostat by grounding the control circuit with a solid state device called a driver. The driver is equipped with a feedback circuit that is pulled-up to a voltage. The ECM can determine if the control circuit is open, shorted to ground, or shorted to a voltage by monitoring the feedback voltage.

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2006 BMW 325i E90 remote programming

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I have a 1989 BMW 325i and it has been overheating so I replaced the thermostat, the housing, cover and the sensors. BUT it it is still overheating. What should I do now??

the problem is in your dash. you are going to have to replace the battery in the instrument panel.
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