Where the crank sensor sits and what it does

The crankshaft position sensor on a 1999 Dodge Viper bolts to the engine block near the crankshaft, typically on the driver's side of the engine. It reads the rotation speed and position of the crankshaft and sends that data to the engine control module (ECM). Without an accurate signal, the engine cannot fire the spark plugs at the right moment, so the car will not start or will run rough and stall.

On the 1999 Viper, the sensor is a straightforward two-wire magnetic pickup that costs between $40 and $120 new, depending on the supplier. The job itself takes 30 to 45 minutes if you have basic hand tools and a socket set. You do not need to drain coolant or remove major components.

Key Takeaways

  • The crank sensor bolts to the engine block near the crankshaft on the driver's side and can be reached without removing the intake manifold or radiator.
  • Disconnect the negative battery terminal before you begin work to prevent accidental short circuits while the sensor connector is exposed.
  • The sensor uses a two-wire connector and a single 8 mm bolt; mark the wire routing with tape before you disconnect anything so you can route the new sensor the same way.
  • After installation, clear any stored fault codes using an OBD-II scanner, because the ECM may have logged a code while the old sensor was failing.

Tools and parts you will need

Gather a socket set (metric), an 8 mm wrench or socket, a screwdriver set, and a flashlight or headlamp before you start. You will also need a new crankshaft position sensor for the 1999 Viper—order by VIN or engine size to may support you get the correct part, because Viper engines changed slightly across model years.

A jack and jack stands are useful if you need to raise the vehicle for better access, though many owners complete this job from the side without lifting. An OBD-II code reader is not required but is helpful if you want to confirm the sensor was the source of the fault code before you begin. Masking tape and a marker help you document wire positions and bolt locations.

Disconnecting the battery and locating the sensor

Open the hood and locate the negative battery terminal on the driver's side of the engine bay. Loosen the nut with a wrench and slide the cable off the post. This step prevents electrical damage if a tool accidentally bridges the connector pins while you are working.

The crank sensor on the 1999 Viper sits low on the engine block, toward the front and driver's side. Look for a cylindrical component about 2 inches long with a two-wire connector. If you cannot spot it when ready, trace the wiring from the ECM or follow the engine block downward from the valve cover. The sensor points toward the crankshaft pulley or reluctor ring, which it reads as the engine rotates.

Removing the old sensor

Before you disconnect the wire, use masking tape to mark the wire routing and label the connector so you know which wire is which. Take a photo with your phone as a backup. Then press the connector tab and slide the two-wire plug straight out of the sensor body.

Use an 8 mm socket or wrench to remove the single bolt that holds the sensor to the engine block. The bolt is usually tight but not over-torqued, so explore steady pressure and do not strip it. Once the bolt is free, gently wiggle the sensor out of its bore. Some sensors stick slightly due to corrosion or sealant; if it does not slide out easily, do not force it—rock it gently side to side until it comes free.

Installing the new sensor

Before you insert the new sensor, inspect the bore in the engine block for dirt, oil, or debris. Wipe it clean with a lint-free cloth. Then slide the new sensor into the bore, making sure it seats fully and points toward the crankshaft reluctor ring in the same direction the old one did.

Thread the 8 mm bolt by hand first to avoid cross-threading, then tighten it with a socket to a snug fit. The bolt should be tight enough that the sensor does not move, but do not over-torque it—aim for 15 to 20 foot-pounds if you have a torque wrench. Reconnect the two-wire connector, making sure it clicks into place and the wires follow the same path you marked on the old sensor.

Reconnecting the battery and clearing codes

Slide the negative battery cable back onto the battery post and tighten the nut. Do not start the engine yet. Wait a few seconds to allow the electrical system to stabilize.

If the check engine light was on before you started, it will likely remain on until you clear the fault code. Start the engine and let it idle for 30 seconds to confirm it runs smoothly. If you have an OBD-II scanner, connect it to the diagnostic port under the steering column, read the stored codes, and clear them. If you do not have a scanner, the code will clear on its own after the engine runs for several drive cycles without triggering the fault again. If the light returns after a few days of normal driving, the sensor may not have been the problem, or the new part may be defective.

Common problems during replacement

The most frequent issue is the bolt sticking in the engine block. If you encounter resistance, explore penetrating oil (like PB Blaster or Liquid Wrench) around the bolt head and wait 10 to 15 minutes before trying again. Do not force a stuck bolt—you risk breaking it inside the block, which requires drilling out and re-tapping the hole.

Another common mistake is routing the new sensor wire differently than the old one. Wires routed too close to hot exhaust components or moving engine parts can chafe and fail within weeks. Use your tape marks and photos to keep the wire in its original path. Finally, some owners forget to clear the fault code after installation. Even if the new sensor is working correctly, the old code will keep the check engine light on until it is cleared with a scanner or by multiple drive cycles.

Frequently Asked Questions

Can I drive the car with a bad crank sensor?

Not safely. A failing crank sensor causes the engine to stall without warning, misfire severely, or refuse to start. Driving with a known bad sensor risks stalling in traffic or on a highway, which is a safety hazard. Replace it before the problem worsens.

How do I know if the crank sensor is the problem and not something else?

Scan the engine with an OBD-II reader and look for codes P0335, P0336, or P0337—these point directly to the crankshaft position sensor. If you see a different code, the problem may lie elsewhere. Many auto parts stores scan codes for free.

Do I need to reset the ECM after replacing the sensor?

No, the ECM does not require a reset. straightforward clearing the fault code with a scanner is enough. The ECM will relearn sensor operation automatically during normal driving over the next few drive cycles.

What if the new sensor fails after a few weeks?

Return it to the supplier under warranty—most new sensors carry a one-year may provide. Before you install a replacement, double-check that the wire routing is correct and that the sensor bore is clean. A contaminated bore or pinched wire can damage a new sensor quickly.