Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSMERCEDES BENZ1989420SELREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMSYSTEM/COMPONENT TESTSFUEL SYSTEMALTITUDE CORRECTION CAPSULE TEST
1989 Mercedes Benz 420SEL
Altitude Correction Capsule Test
1989 Mercedes Benz 420SELSECTION Altitude Correction Capsule Test
- Disconnect plug on altitude correction capsule (located near CIS-E under dash on passenger's side). Turn ignition on. Check voltage between terminal Nos. 2 and 3. Voltage should be about 5 volts. If voltage is not about 5 volts, check power supply and ground according to wiring diagram. If okay, go to next step.
- Turn ignition off. Check wire between altitude correction capsule plug (terminal No. 1) to CIS-E control unit plug (terminal No. 11) for continuity. Resistance should be about zero ohms. If resistance is not about zero ohms, repair open circuit. If okay, go to next step.
- Start engine and run at idle speed and at operating temperature. With On-Off Ratio Tester (KDJE-P 600) connected at test socket on left side of engine compartment, the on-off ratio needle should oscillate. If needle does not oscillate, replace altitude correction capsule. If okay, test is complete.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.