Warm-up regulator 0438140061 W126 R107 380 models: Symptoms & replacement
If you drive a W126 380 SE or an R107 380 SL with K-Jetronic, you know the picture: in the morning the car is hard to start, for the first few minutes it runs roughly, and when warm it suddenly smells of gasoline. Many people then first replace the spark plugs or the cold start valve. Often, though, the warm-up regulator is behind it – the component that, in the K-Jetronic, determines the control pressure and thus the mixture during the warm-up phase. In this guide you will learn how to narrow down the fault and what matters when replacing the 0 438 140 061.
Symptoms
| Symptom | Likely cause |
|---|---|
| Engine starts when cold but runs roughly for the first few minutes or stalls | Control pressure too high when cold – warm-up regulator does not kick in, mixture too lean |
| Black smoke when warm, smell of gasoline, high consumption | Control pressure too low when warm – heater or bimetal in the regulator defective |
| Popping or hesitation when accelerating briskly | Mixture enrichment via the regulator is missing, possibly vacuum connection leaking |
| Damp spots on the banjo bolts of the regulator | Seals aged – fuel leak, fix immediately |
| Does not start at all when cold, only brief firing while cranking | More likely cold start valve or thermo time switch – see Cold start valve: testing and replacing |
| Poor hot start when warm after a short standstill | More likely fuel accumulator, check valve or fuel pressure regulator – see Fuel pressure damper K-Jetronic W116/W126 |
Causes
The warm-up regulator works with a bimetal spring heated by an electric heating element. When cold, the spring presses less firmly on the diaphragm valve, the control pressure drops, and the K-Jetronic enriches the mixture. As it warms up, the control pressure rises to its operating value. After several decades, three types of damage mainly occur: the heating element burns out or has contact resistance at the connector, the diaphragm and seals harden from fuel and heat, and deposits from old fuel interfere with the fine valve. The result is a control pressure that no longer suits the engine, cold or warm.
Testing it yourself
- Visual inspection: Check the regulator, banjo bolts and fuel lines for damp spots and cracks, and check the vacuum hose (if present) for porosity.
- Connector and voltage: Pull the connector and check the contacts for corrosion. With the engine running, vehicle system voltage must be present at the connector.
- Measure heater resistance: Use a multimeter to measure the resistance of the heating element. No continuity means: heater defective. Take the specified value from the workshop manual.
- Check the warm-up: After a few minutes of engine running, the regulator must warm up noticeably. If it stays cold, it does not regulate to operating pressure.
- Measure the control pressure: Measure the control pressure cold and warm with a K-Jetronic pressure gauge and compare it with the specified values. Only this measurement proves the defect unambiguously. You can find more on the procedure in our guide Warm-up regulator defective – symptoms and testing.
Solution
If the regulator is defective, replacing it with a tested genuine part is the cleanest solution. We offer the Bosch warm-up regulator 0 438 140 061 for the 380 models with M116, remanufactured: genuine part, not aftermarket, heating resistor and seals renewed, individually tested and with a 5-year warranty. Price: 499,00 €. Please compare the number on the type plate of your removed regulator before buying. After installation, we recommend checking the control pressure as well as idle speed and CO value.
This part is a single item. Once it is sold, you can find more injection parts in our category Fuel system & injection as well as matching parts for the S-Class at W126 and for the SL at W107 / R107.
Bosch warm-up regulator 0 438 140 061
Remanufactured · Mercedes 380 SE/SEL/SEC, 380 SL/SLC · M116 K-Jetronic
499,00 €
To the warm-up regulatorCompatible vehicles
| Model series | Model | Engine |
|---|---|---|
| W126 (126.032 / 126.033) | 380 SE, 380 SEL | M116 |
| C126 (126.043) | 380 SEC | M116 |
| R107 (107.045) | 380 SL | M116 |
| C107 | 380 SLC | M116 |
Note: What counts is the Bosch number on the type plate of your regulator. Other engine variants may use different warm-up regulators.
FAQ
Which warm-up regulator fits the Mercedes 380 SE, SEL, SEC and 380 SL/SLC?
The Bosch warm-up regulator 0 438 140 061 is specified for the 380 models with the M116 engine and K-Jetronic – according to the product data, it fits W126 380 SE/SEL, C126 380 SEC and R107/C107 380 SL/SLC. Compare the number on the type plate of your old regulator before buying.
How do I recognize a faulty warm-up regulator?
Typical signs are poor cold-start behavior, jerky running during warm-up, running too rich with black smoke and high consumption when warm, or a lean popping when accelerating. The defect is only reliably proven by a control pressure measurement cold and warm.
Can I test the warm-up regulator myself?
Yes. Power supply at the connector, heater resistance and vacuum connection can be checked with a multimeter and visual inspection. For the control pressure measurement you need a K-Jetronic pressure gauge and the specified values from the workshop manual.
What was done to the overhauled warm-up regulator?
It is a remanufactured genuine Bosch regulator, not aftermarket. The heating resistor and seals were renewed, and the regulator was individually tested. According to the product description, the part carries a 5-year warranty.
Does anything need to be adjusted after replacement?
After installation you should check the control pressure cold and warm and then have idle speed and CO value checked or adjusted, since the mixture preparation changes compared with the worn regulator.
KFZTeile-Thot is a specialist company for tested and refurbished Mercedes parts with its own test benches. Over 1,000 positive eBay reviews stand for carefully tested parts. Not sure whether the regulator fits your vehicle? Call us at +49 179 8991069 (Mon–Fri 8 am–6 pm) or write to us via the contact form.