Qashqai engine light with P0597: how I found the faulty thermostat.

The car

A 2017 Nissan Qashqai 1.2 DIG-T, petrol, 38,000 miles. Engine light on.

The first scan found 37 stored codes. Most of them were left by a flat battery after the car had sat for about a year. One was a real fault: a misfire on cylinder 4. Its counter read 1,440 while the other three read 2, 0 and 8. I cleared the codes, and the oil and filters were changed at the service.

The rescan after the service was down to 7 codes, and only one was live: P0597-13, thermostat heater control circuit open.

What P0597 means

On this engine the engine computer heats an element inside the thermostat, so the thermostat can open earlier when the engine is working hard. P0597 says that heater circuit is open. On this car it wasn't the fuse.

What I tested

The wiring was fine. The old heater read about 14 times the new one, which the engine computer sees as an open circuit. So the fault was inside the thermostat.

The job

The thermostat housing is buried, so the intake manifold has to come off to reach it. While it was apart I cleaned the manifold's mating face and the throttle body. New thermostat in, then the coolant bled from both bleed screws.

After the job I cleared the codes and ran the engine up to temperature four times: no engine light, no overheating, and hot air from the heater.

If your Qashqai shows P0597

Test the wiring first. If the feed and the engine computer's side read right, the fault is inside the thermostat, and on this engine that's a manifold-off job, so you want to be sure before you start.

How I got these readings: on the job, with a full-system scanner and a multimeter, before and after.

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