2002 Volvo V70 2.4L Non-Turbo with P0128: Coolant Temperature Sensor & Fan Issues at 75k Miles

The engine revving and fan failure may not be directly linked to P0128, but the code typically points to a slow warm-up due to issues with the thermostat or coolant temperature sensor. Replacing these components is a logical first step. If stalling persists, please update your situation. The cooling fan should be checked immediately — failing to operate can lead to engine overheating, which may damage internal components over time.

It's worth considering whether coolant flow is restricted through the throttle body — a known issue in older Volvo models like the Talon. Low coolant levels can cause surging or erratic engine behavior, especially under load.

That’s a solid point — thanks for highlighting that possibility. I hadn’t considered throttle body-related coolant flow as a factor before.

Jeff Compton wrote: 'Unless it's a coolant flow problem through the throttle body like the old Talons had! When they were low in coolant, they'd surge!' Funny you mention that — about six months ago, I was refilling coolant every 2 to 3 months. Now, I haven’t needed to refill at all. No puddles under the car have been observed.

It’s important to check your current coolant level — even if there's no visible leak. If you're not refilling regularly and the level is stable, it could indicate a hidden coolant consumption issue. Combined with an inoperative cooling fan, this raises concerns about potential overheating or internal engine problems like a blown head gasket.

I'm new to this forum and the issue seems old — but I had a similar experience with my 1995 Volvo 850 Turbo after radiator work. It took months and several expensive parts to realize that the root cause was often a high-resistance connection in the temperature sensor circuit. The standard mechanic might miss it because of how Volvos are built. Volvo sensors and relays use plastic connectors with potting compound that holds metal contacts securely. Over time, this compound degrades — leading to poor pin alignment or back-insertion during reconnection. This creates high resistance, which confuses the ECU and can trigger symptoms like P0128, stalling, and erratic behavior. I recommend checking all sensor connectors, cleaning contact points, and ensuring wires are properly seated. If the potting compound is gone, incorrect reinsertion could be causing intermittent faults.

This isn’t a clog per se — but there are several possible root causes. First, check your current coolant level and reservoir status. If it's low, that suggests either a leak or engine coolant consumption. A failing fan can lead to overheating, which may result in head gasket failure and subsequent coolant loss. Low coolant levels directly contribute to P0128 and erratic engine behavior like revving and stalling.

I’ve been researching this issue for a while — the root cause in many Volvo cases is not mechanical failure, but poor electrical connections. The potting compound inside sensor connectors deteriorates over time, especially after repeated disconnections. When reconnected incorrectly or with degraded contact points, it creates high resistance and sends faulty signals to the ECU. This can mimic P0128, stalling, and engine revving issues. Always inspect all sensor connectors — clean contacts thoroughly, ensure proper alignment, and avoid forcing wires back into place. This is a common but overlooked fix in Volvo repairs.