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Chrysler ECU Computer Code 16: Battery Voltage Drop Below Normal

by Bob O'Neill and Bob Lincoln

When the engine is running and there is a loss of battery voltage detected, a code 16 is set. Code 16 will be set a minute after the engine starts and the voltage sense input at the ECU is below 8.5v.

If the voltage at the ECU voltage sense input is between 4v and 8.5v, the alternator field coil will be set to full field or 100% duty cycle for 20 seconds. If after this time the voltage sense voltage is still below 8.5v the ECU will enter limp mode and turn on the Power Limited light as well as set code 16. At this point the alternator will be set to a fixed 25% duty cycle. This will prevent overcharging the battery yet still allow it to operate.

Possible reasons for code 16

Fusible link to power module (or SMEC) disconnected or blown - The white fusible link feeds power to ECU or SMEC. It may be gray due to the dirt it has been exposed to. Check the fusible link by checking for breaks in the link. When you pull on it the link will feel solid if it's good. If it feels like a rubber band it's blown. The one you want to check is the white link in the two link circuit not the one with four or five links. This is the same link that provides power to the ASD relay and of course the voltage sense input on for the ECU/SMEC. Also see code 42. (If a fusible link to the power module has blown, both code 42 and code 16 may be set).

Poor connection or bad wiring - Read 'How to troubleshoot drivability issues'. The wiring and connections between the alternator and the battery should be checked. Also check the connections between the power module and the alternator field coil, and the voltage sense line through the power and logic modules.

Defective alternator or voltage regulator circuit - To make these tests the engine must be running. If necessary jump start the car from another car and once running disconnect the other car. With the engine running and disconnected from any assistance used to get it started, measure the voltage across the battery terminals. If your voltage measurement is between 13.3v and 14.7v then the problem is not the charging system. If this is the case the battery or the battery terminals are suspect.

Another test is to measure the voltage across the output terminals of the alternator. The large lower terminal is the negative terminal and the large upper terminal is the positive terminal. The voltage across these should also measure between 13.3v and 14.7v. A measurement of below 12.8v indicates that the alternator is undercharging and a measurement of over 14.7v indicates that the alternator is over charging. Should the voltage be under 12.8v when measuring at the battery but at the alternator the measurement is within range then the problem is either the battery or the connections at the battery terminals.

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