Chevrolet Sonic: thermostat, its sensors and error 89 (P0597)

On the latest generation of Chevrolet Sonic T300 engines, it is quite common to encounter problems with thermostats, their housings and sensors. The onboard computer can show error code 89 on the onboard display, and when you connect a scanner or a laptop through an adapter, you get error code P0597. We solve this problem radically.

What is error code 89 (P0597) on Sonic T300, consequences

Let’s briefly consider why error P0597 occurs on the Chevrolet Sonic t300 and what it can lead to if the issue is not fixed in time. First, about sad things.

Ignoring error 89 (P0597), we jeopardize the temperature regime of the engine. This is fraught not only with frequent overheating, but also with the failure of a number of parts:

The electronic engine control unit controls the thermostat using pulse width modulation signals. The Chevrolet Sonic t300 has an antifreeze heater in the thermostat housing. It regulates the coolant flow and controls the temperature mode.

The ECU must permanently supply 12 V to the thermostat and control the heater by connecting it to the engine ground. Connection is made via semiconductor signal conditioner. It has a feedback circuit connected to the common 12 V supply.

The ECU controls the entire unit by reading the heater feedback voltage. Thanks to this circuit, ECU easily calculates the functionality of the whole thermostat and can detect both short to ground and open circuit, which is signaled to the driver with a fault code.

Also, if we have a scanner or PC at hand, in addition to the error P0597 we can get related error codes – P0598 and P0599.

These are clarifying codes, which can be decoded as follows:

1. P0597 – open circuit in the thermostat heater circuit.
2. P0598 – Under voltage of thermostat heater.
3. P0599 – Over-voltage reading.

In short, it is clear that when code 89 or error P0597 appears on the BC display on the Sonic T300, our task is to check or get rid of the antifreeze heater, if possible.

Chevrolet Sonic thermostat issues

Unfortunately, this is not the only problem with this thermostat. The same problem accompanies owners of not only Sonic, but also Chevrolet Cruze and a number of other models with similar Opel family tree.

Another issue is the plastic thermostat housing. Its quality and the quality of the rubber seals do not stand up to criticism. After 20-25 thousand miles, the thermostat bodies start to bleed antifreeze from all possible slots.

Fighting the leak, as a rule, does not bring success, so the only true solution in this situation is to replace the plastic housing with a metal one.

There are also questions about the thermostat valve. As standard, it opens at 104 °C and cycles through the temperature range down to the lower limit of 98 °C. In theory, the mechanical valve is installed as a backup if the electrical part fails.

However, many people deliberately decide to buy a thermostat housing without a heater, saving themselves from future problems with electronics. This is what a thermostat enclosure like the one shown in the photo is for.

And so that the electronic control unit does not resent the absence of the heater, a jumper is installed on the terminal block. Faults in the electrical part occur against the background of a constantly turned on radiator cooling fan.

In this mode of constant work, it will not last long – the bearings will crumble. It is possible to put a new fan, but it will meet the same fate as the previous one, if the issue is not solved radically. To prevent the fan from working in emergency mode, some changes are made in the firmware of the electronic control unit, which will get rid of such issues forever.

Yes, many people also prefer to install a cooler thermostat with an opening temperature of 92 °C on the Chevrolet Sonic. For example, the Borg Wagner, which has no heater.

This is what we get if we put the thermostat without heating and correct the firmware:

1. It is possible to update the firmware to the latest stock firmware.
2. No need to put a resistor in the heater connector, it is disabled by software.
3. The radiator fan works in normal mode, not in emergency mode.
4. The cooling system works more efficiently and safely, which affects the dynamics, fuel consumption and engine life of the Sonic T300.

Thermostat Chevrolet Sonic. Checking the heater and P0597 error

Однак, перед такою роботою варто перевірити нагрівач термостата. Тестування проводимо у такому порядку:

1. Turn off the ignition and disconnect the connector from the thermostat heater.
2. Switch on ignition. Check if ECU is supplying power to the heater. Voltage must be between the second contact of the connector and the engine ground. You can use a test lamp or multimeter to check it. If there is no voltage, first of all check wiring for breakage or short circuit.
3. The low signal circuit (pin #1) should not indicate any voltage.

   

4. Switch off ignition. Disconnect the terminal block from the ECU and check the resistance between pin #43 and the ground. Resistance should tend to infinity.
5. Check resistance between pin #43 of ECU connector and pin #1 of the thermostat heater connector. The nominal value is at least 5 ohms.
6. If all circuits are checked, replace the thermostat heater. It is sold separately from the housing.

Or do as described above – throw out the heater and install Borg Wagner thermostat valve without heating element. If there is no possibility to flash the ECU, between the contacts of the heater pad install a resistance (150 ohms) or a relay.

Changing the thermostat on the Chevrolet Sonic

The job of replacing either the thermostat housing or the valve itself with the heating element (or without it, as desired) is done in an hour with a good tool and straight hands.

Replacement will require new gaskets and gaskets, which can be found by catalog numbers:

1. 55353353 GM, rectangular thermostat housing gasket.
2. 1338351 GM, thermostat valve body gasket.
3. 1338351 GM, drain tube o-ring.

And also those elements which we are going to change – thermostat body, antifreeze distributor body (plastic or metal), thermostat for 92 or 104 degrees and, probably, sealant.
First we drain the antifreeze into the prepared container by removing the socket on the body.

When the antifreeze drains (it is about 350-400 g), take the branch pipe aside.

Remove the expansion tank, so it does not interfere. It is not necessary to disconnect it, just take it aside.

Unscrew the 4 thermostat mounting bolts and remove the valve and heater assembly.

All that remains is to check the condition of the gaskets and install a new thermostat. Connecting everything in place, pouring antifreeze, checking the system’s operation.