This procedure requires the use of the following special tools, or their equivalents:
MB991958: Scan Tool (MUT-III Sub Assembly)MB991824: V.C.I.MB991827: MUT-III USB CableMB991910: MUT-III Main Harness A
Before starting the check, make sure that the vehicle is in the following condition:
- Engine coolant temperature: 80 - 95°C (176 - 203°F)
- Lights and all accessories: OFF
Transaxle: Neutral (or P range on vehicles with A/T)
NOTEOn Canadian vehicles, the headlight, taillight, etc. remain lit even when the light switch is in the "OFF" position. This is not a problem for checks and adjustment.
WARNINGTo prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
- Connect the scan tool to the data link connector.
Set the timing light to the power supply line (terminal No. 1) of the No. 1 ignition coil.
NOTEThe power supply line is looped and also longer than the other ones.
- Start the engine and allow it to idle.
- Check that the idle speed is about 680 rpm.
Select scan tool MB991958 actuator test "item number 17".
- Check that base ignition timing is within the standard value: 2-8°BTDC (Before Top Dead Center).
If the base ignition timing is not within the standard value, check the following:
- Diagnostic output
- Timing belt cover and crankshaft position sensor installation conditions
Crankshaft sensing blade condition
WARNINGIf the actuator test is not canceled, the forced drive will continue for 27 minutes. Driving in this state could lead to engine failure.
- Press the clear key on scan tool MB991958 (select forced drive stop mode), and cancel the actuator test.
Check that the actual ignition timing is at the standard value: about 10°BTDC.
NOTEIgnition timing fluctuates approximately +/- 7°Before Top Dead Center, even under normal operating conditions.
NOTEAt higher altitude, ignition timing is automatically further advanced by about 5-10°BTDC.