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SPN 110 — Coolant temperature

Updated: 2026-11-10

Do not driveMinutes

J1939 code SPN 110. Below — how the fault is worded at the factory by Cummins ISB, DAF, Dongfeng, Foton, Isuzu, KAMAZ, KAMAZ-5490, MAZ, Renault Trucks, SITRAK, YaMZ and ZF AS-Tronic, and what the second half of the code (FMI) means in the standard.

Detailed breakdown

How to check it yourself

The coolant temperature sensor sits in the thermostat housing or in the cylinder head. It is a two-wire thermistor (NTC): the hotter it gets, the lower its resistance. The ECU uses it to decide how much fuel to give on start, when to switch on the fan, and when to cut power for overheating.

What it should read

Resistance of a typical NTC sensor at 20 °Cabout 2…3 kΩ
The same at 80 °Cabout 300 Ω — more precisely per the factory table
Voltage at the harness connector with the sensor unpluggedabout 5 V
Warm engineusually 80…95 °C

Check order

  1. FMI 0, 15, 16 (temperature high): check the engine first, not the sensor. Coolant level in the expansion tank, belt and fan clutch, radiator clogged with dirt on the outside, tank cap.
  2. Compare the dash reading with an infrared thermometer on the top radiator hose. If they agree — the overheating is real.
  3. FMI 3, 4: unplug the connector and measure the sensor resistance. An open sensor or wire is seen by the ECU as −40 °C frost (voltage high, FMI 3), a short as severe overheating (FMI 4). With the connector unplugged, the harness contacts should show about 5 V.
  4. Compare the diagnostics reading on a cold engine that has stood overnight with other temperatures: air, oil, coolant. All should be close to the outside temperature; one lagging 10 °C or more is suspect.
  5. FMI 1, 17, 18 (not warming up): a thermostat stuck open — especially in winter at idle.

Common causes — from most to least frequent

  1. Real overheating: low coolant, dirty radiator, fan clutch, water pump.
  2. Thermostat stuck open or closed.
  3. Corroded sensor connector.
  4. The sensor itself.
  5. Air lock after a coolant change.

Cummins ISBDAFDongfengFotonIsuzuKAMAZKAMAZ-5490MAZRenault TrucksSITRAKYaMZZF AS-Tronic

Cummins ISB 6.7 engine

FMI 0Engine coolant temperature high, most severe
FMI 2Engine coolant temperature signal erratic or incorrect
FMI 3Engine coolant temperature sensor circuit voltage high
FMI 4Engine coolant temperature sensor circuit voltage low
FMI 15Engine coolant temperature high, least severe
FMI 16Engine coolant temperature high, moderately severe
FMI 18Engine coolant temperature: below normal range, moderately severe
FMI 31Engine coolant temperature condition exists

DAF

FMI 0Coolant temperature F566 too high, engine protection active
FMI 2Coolant temperature F566 out of range at ignition on (extended period)
FMI 3Coolant temperature F566 short to power supply at ECU pin A49 (extended period)
FMI 4Coolant temperature F566 short to ground at ECU pin A49 (extended period)
FMI 15Coolant temperature F566 temperature too high

Dongfeng

FMI 0Engine coolant temperature too high
FMI 2Incorrect coolant temperature signal. Scan tool code: P0116.
FMI 3Short circuit to power or open circuit of the coolant temperature sensor
FMI 4Short circuit to ground of the coolant temperature sensor
FMI 15Engine coolant temperature too high (minor)
FMI 16Engine coolant temperature too high (minor)

Foton

FMI 15Coolant temperature above allowed limit

Isuzu

FMI 0Overheat (P1173)
FMI 3Engine coolant temperature sensor fault (high voltage fault) (P0118)
FMI 4Engine coolant temperature sensor fault (low voltage fault) (P0117)

KAMAZ engine (J1939)

FMI 0Coolant temperature sensor: physical range limit.
FMI 1Coolant temperature sensor: physical range limit
FMI 2Coolant temperature sensor
FMI 3Coolant temperature sensor.
FMI 4Coolant temperature sensor.
FMI 12Coolant temperature sensor
FMI 14Coolant temperature (from PLD/MR2).
FMI 15⚠ Coolant overheating

KAMAZ-5490 (Mercedes, K-line)

FMI is per the block maker's own table, not the J1939 table below.

FMI 0Coolant temperature sensor: coolant temperature high. K-line code on KamAZ-5490: MR2 12122.
FMI 3Coolant temperature sensor: short to high. K-line code on KamAZ-5490: MR2 11515.
FMI 4Coolant temperature sensor: short to low. K-line code on KamAZ-5490: MR2 11516.
FMI 14Coolant temperature (from PLD/MR2): coolant temperature too high. K-line code on KamAZ-5490: ADM3 10914.

MAZ

FMI 2Coolant temperature sensor circuit fault - Reading inconsistent with the oil temperature reading. Blink code: 2-4-1. Power will be reduced. Repair: Check the coolant temperature sensor and its wiring.
FMI 3Coolant temperature sensor circuit fault - Voltage above allowed. Blink code: 2-4-1. Power will be reduced. Repair: Check the coolant temperature sensor and its wiring.
FMI 4Coolant temperature sensor circuit fault - Voltage below allowed. Blink code: 2-4-1. Power will be reduced. Repair: Check the coolant temperature sensor and its wiring.
FMI 12Coolant temperature sensor circuit fault - CAN bus signal implausible. Blink code: 2-4-1. Power will be reduced. Repair: Check the coolant temperature sensor and its wiring.
FMI 15Coolant overheating - Overheating. Blink code: 2-4-2. Repair: Check the radiator.

Renault Trucks

FMI 3Coolant temperature sensor — short to positive (5 V or battery voltage). Repair: Check the sensor and the wiring (J 1/17, J 1/26). Check the sensor and the engine wiring (A 1, A 30).
FMI 4Coolant temperature sensor — short to ground. Repair: Check the sensor and the wiring (J 1/17, J 1/26). Check the sensor and the engine wiring (A 1, A 30).
FMI 5Coolant temperature sensor — open circuit; check the engine wiring and the sensor itself. Repair: Check the sensor and the wiring (J 1/17, J 1/26). Check the sensor and the engine wiring (A 1, A 30).
FMI 15Coolant temperature above normal. Repair: Check the sensor and the engine wiring (A 1, A 30).

SITRAK

FMI 0Coolant temperature above torque limit class 2
FMI 2Coolant warm-up not plausible: the temperature does not reach the threshold in time. Scan tool code: P0116.
FMI 3High voltage on coolant temperature sensor
FMI 4Low voltage on coolant temperature sensor
FMI 15Coolant temperature above torque limit class 1
FMI 17Coolant warm-up not plausible: the temperature does not reach the threshold in time. Scan tool code: P0116.
FMI 18Coolant warm-up not plausible: the temperature does not reach the threshold in time. Scan tool code: P0116.
FMI 19Timeout of the coolant temperature CAN frame. Effect: Fan and warm-up control may misbehave.
FMI 20Coolant overheating downstream of the engine, threshold 1. Scan tool code: P0115. Effect: Fan and warm-up control may misbehave.
FMI 21Coolant overheating downstream of the engine, threshold 2. Scan tool code: P0115. Effect: Fan and warm-up control may misbehave.
FMI 22Coolant overheating downstream of the engine, threshold 3. Scan tool code: P0115. Effect: Fan and warm-up control may misbehave.

YaMZ

FMI 2Coolant temperature sensor circuit fault (Reading inconsistent with oil temperature reading). Blink code: 2-4-1. Power will be reduced. Repair: Check the coolant temperature sensor and its wiring.
FMI 3Coolant temperature sensor circuit fault (Voltage above allowable limit). Blink code: 2-4-1. Power will be reduced. Repair: Check the coolant temperature sensor and its wiring.
FMI 4Coolant temperature sensor circuit fault (Voltage below allowable limit). Blink code: 2-4-1. Power will be reduced. Repair: Check the coolant temperature sensor and its wiring.
FMI 12Coolant temperature sensor circuit fault (CAN bus signal implausible). Blink code: 2-4-1. Power will be reduced. Repair: Check the coolant temperature sensor and its wiring.
FMI 15Coolant overheating. Blink code: 2-4-2. Repair: Check the radiator.

ZF AS-Tronic gearbox

FMI is per the block maker's own table, not the J1939 table below.

FMI 0ZF-CAN bus timeout.

What FMI means in J1939

SPN 110 FMI 0110/0 · 110.0data above normal range (most severe level)
SPN 110 FMI 1110/1 · 110.1data below normal range (most severe level)
SPN 110 FMI 2110/2 · 110.2data erratic or intermittent
SPN 110 FMI 3110/3 · 110.3voltage above normal or shorted high
SPN 110 FMI 4110/4 · 110.4voltage below normal or shorted to ground
SPN 110 FMI 5110/5 · 110.5current below normal or open circuit
SPN 110 FMI 12110/12 · 110.12faulty device or component
SPN 110 FMI 14110/14 · 110.14manufacturer-specific instructions
SPN 110 FMI 15110/15 · 110.15above normal — low severity
SPN 110 FMI 16110/16 · 110.16above normal — moderate severity
SPN 110 FMI 17110/17 · 110.17below normal — low severity
SPN 110 FMI 18110/18 · 110.18below normal — moderate severity
SPN 110 FMI 19110/19 · 110.19error in received network data
SPN 110 FMI 20110/20 · 110.20data drifted high
SPN 110 FMI 21110/21 · 110.21data drifted low
SPN 110 FMI 31110/31 · 110.31condition exists (see manufacturer description)

Can I keep driving

Do not drive. Stop as soon as it’s safe to do so — don’t keep going.

What happens if you keep driving

Time you have: Minutes

The engine is already past its temperature limit. An aluminium head goes fast: first the geometry warps, then the gasket burns through.

Next comes a blown head gasket, a damaged head and, at worst, a cracked block. Shut it down and let it cool — never open the expansion tank cap while hot.

This is an electrical fault: the sensor or its wiring is lying, not the cooling system. The temperature gauge is unreliable now and the fan may not kick in on time. Watch the coolant level and keep the engine off load on long climbs.

What to check on the spot

Let the engine cool — never open the expansion tank cap while hot. Then check the level and the hoses.

Which codes follow

If the value really did go out of range, rather than a sensor circuit being broken, these normally light up after it:

They are not fixed separately — they go out together with this one. The list is deliberately short: only the links the reference is sure about.

Makes with this code

KAMAZMAZYaMZSITRAKDongfengFotonDAFRenault TrucksIsuzuCummins ISBKAMAZ-5490

Related problems

What SPN 110 and its FMI tell you

SPN 110 is engine coolant temperature in SAE J1939. The sensor is a thermistor in the cylinder head or the coolant outlet: its resistance falls as it gets hotter. The engine computer uses it to switch the fan on, to derate power and, in the worst case, to shut the engine down.

Causes of a real overheat, most common first

How to check

1. Stop and let the engine cool before opening the cap. Check the level in the expansion tank and look for drips.

2. Compare the scan-tool temperature with reality. After a cold night it should equal the ambient temperature. If it does not, the sensor or its circuit is at fault.

3. With the engine warm, listen for the fan engaging and feel the hoses (carefully): hot upper and cold lower hose points to a closed thermostat.

4. For FMI 3 and 4, inspect the sensor connector for corrosion and test the sensor against the manual's resistance table.

Normal operating temperature on most diesels is roughly 80-95 C; check your engine manual for exact limits.

Can you keep driving?

Not with FMI 0 or a red coolant lamp: a few minutes of overheating can warp the head. Pull over and let the engine cool. With FMI 15 or 16, find a safe place and diagnose; driving on with a climbing gauge is how head gaskets fail. With FMI 3 or 4 the engine may be fine, but the over-temperature protection is blind, so watch the dash gauge closely.

Questions and answers

It only overheats on hills. Is that SPN 110?

The code is only the reporter. The cause is usually a radiator or fan that cannot keep up under load: check the fins, the fan clutch and the thermostat.

The gauge reads far too cold or too hot right after starting. Why?

That points to an open or shorted sensor circuit (FMI 3 or 4). Check the connector and wiring, then the sensor.

Can I top up with plain water to get home?

Only as an emergency measure to reach the nearest safe stop, and only after the engine has cooled. Plain water lowers corrosion protection and the boiling point margin.

Scanner threw several codes at once? Paste the whole list — we will show which one is the root cause and which ones simply followed.