Start the Engine With a Dead Key Fob

The Dodge Magnum (LX, 2005–2008) wagon is a turn-key car — you insert a transponder cut key (a remote-head key on most builds) into the ignition barrel and twist. There is no push-button start on the Magnum, so a flat key-fob battery is a minor annoyance rather than a breakdown: the engine still starts normally. Only the lock, unlock and liftgate buttons stop working until you fit a fresh cell.

A Flat Fob Battery Does Not Stop the Magnum Starting

The coin cell inside the remote-head key powers only the radio buttons. Starting runs through the Sentry Key immobiliser, which reads a passive transponder chip moulded into the key head — and that chip carries no battery of its own.

1. If the remote buttons are dead, unlock the driver’s door manually with the key blade.
2. Push the key fully into the ignition barrel on the steering column.
3. Twist to start as usual. The immobiliser energises the chip, reads its code, and the engine cranks and runs.

So on the LX Magnum a dead fob never leaves you stranded — you simply lose the remote buttons until the cell is replaced.

Unlocking the Door by Hand

1. Use the cut key blade — on most Magnums it is the same key you turn in the ignition. On a separate-blade fob, slide the latch and draw the emergency blade out.
2. Insert it into the driver’s door lock cylinder and turn to unlock.
3. If the alarm chirps as you open up, turning the key in the ignition to start clears it.

Why the Immobiliser Ignores the Fob Battery

An antenna ring around the ignition barrel powers the transponder chip by induction, so the chip can answer even with a completely flat coin cell. The engine-control module only lets the Magnum run once it recognises that chip’s code — which is why a flat fob affects the buttons but never the start.

Fitting a New Coin Cell

1. Split the remote-head key case at the seam with a small flat screwdriver.
2. Most 2005–2008 Magnum keys take a CR2032 3 V lithium coin cell — check the old one to be sure.
3. Fit the new cell the same way up (positive usually faces the cover), clip the case shut and test the buttons beside the car.

Frequently Asked Questions

Does the Magnum have push-button start? No — every 2005–2008 Magnum is turn-key. Keyless push-button start never came to this wagon.

The key turns but the engine starts then stalls, with the security light flashing. That is an immobiliser fault — a failed transponder or a key not matched to the car — not a flat fob. The coin cell has no bearing on starting.

Which battery does the Magnum key take? A CR2032 on most builds; confirm against the old cell.

The remote stopped but the wagon starts fine — is that a problem? No — that is exactly how a flat key battery shows up here. Fit a new CR2032 to restore the buttons.

Can a blank key start it? No — a plain blade turns the locks but the immobiliser blocks the engine without a programmed chip.

If a warning light stayed on after you drove off, look the fault code up on our sister site autodtcs.com to see whether it points at the immobiliser or something else.