By on January 31, 2020

Diana writes:

Hi Sajeev!

My husband, rrhyne56, gave me your email address, because I have a question about my 2008 Honda CR-V.

The alarm goes off, in the middle of the night, only when the temperatures are freezing. Unlocking with the FOB, stops it. But, the FOB will not lock the car. I have to open the door, close it and then the FOB will lock and set the alarm again.

Hope you can help, because I’m losing sleep. Maybe my car wants us to move to a warmer place… 😉

Sajeev answers:

I don’t work on commission, yet I love getting referrals!

Assuming this is a factory Honda alarm, I’ll bet there’s a bad door/hood/hatch sensor freaking out the system. The Internet says a weak battery is a major concern, so ya better test that first. 

If the battery passes but there was recent collision repair, I reckon the affected area also needs a new sensor. More to the point, after I wrecked my Mark VIII, one of the first things I did was disconnect the hood sensor: it mercilessly honked as I tore off damaged panels. Since my diagnosis was pretty damn obvious, I bought an NOS Ford sensor and cleared one of the easier hurdles on that project.

If the CR-V has no recent collision repair, either disconnect or clean the sensors. I couldn’t google the Honda diagnostic, but the logic is to disconnect a sensor, tricking the computer into thinking everything is fine. The trick might also entail jumping the wiring with a metal paperclip. Watch this video, ask someone smarter than me and/or experiment yourself by starting without the paper clip.

I reckon you need a new hood sensor, as it had enough of having a hood slam down on it. I certainly don’t want that thing slamming down on me for 12 years.

What say you, Best and Brightest?

[Image: Honda]

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice. 


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35 Comments on “Piston Slap: Sounding the Alarm on a Bad Sensor?...”

  • avatar

    Did you mis-speak (or more properly mis-type) Sajeev? It seems the door sensor – if present – would be the first one to check instead of the hood sensor as “unlocking with the fob” stops the alarm. Other than that your trouble shooting steps should provide a successful resolution of the issue.

    • 0 avatar

      Locking and unlocking the doors shouldn’t affect the sensors. They’re push pins that only move when the door is physically moved.

      If they’re all in position and move properly, it’s hard to imagine how they’d spontaneously close a circuit. Maybe there’s an intermittent short somewhere around one but they’re so simple I’d lean toward a battery issue.

      Troubleshooting shouldn’t be too difficult, anyway. One could even just start by disconnecting them all.

      • 0 avatar

        What’s happening is, a door switch is failing intermittently in such a way that tells the currently active alarm system that “someone opened the door, the door is now open but the alarm wasn’t turned off”. That makes the alarm sound.

        She hits the “unlock doors” with her remote; that tells the alarm system that “owner is here, all is well, stop wailing the alarm and turn the alarm system off”.

        When she tries to lock the car, she can’t–because that door switch is still telling the car that “I’m open, the door is open”. And when the door is open, you can’t use the remote to lock the car.

        This is a simple failing door switch. Not rocket science.

        • 0 avatar

          “What’s happening is, a door switch is failing intermittently in such a way that tells the currently active alarm system that “someone opened the door, the door is now open but the alarm wasn’t turned off”. That makes the alarm sound.”

          You can replace door switch with hood sensor and the same will apply. They all trigger the same reaction to the alarm.

        • 0 avatar

          I believe you are correct. When I drive at night, which isn’t often, the interior light comes on, when I make a left turn. Crazy right?
          Also, I tend to press my leg against the door slightly when I drive. This slight pressure sets the interior light off too.

          In cold weather, what happens to material objects? They contract slightly. I think the cold weather contracts the door just enough, that the door switch loses contact and ….. Beep Beep Beep… wake up everybody!

          Thanks for turning the light on for me, with your comment.
          Getting door switch replaced… car wash dudes broke the original completely off, wiping down interior of door. This one is a replacement.
          Thanks Sajeev, for posting my problem.

  • avatar

    Sell the junker

  • avatar

    You drive a 2008 CR-V? No no no, you’re doing it wrong! The secret to maximizing your Honda’s reliability is to trade it in for a new one after 3 years

  • avatar
    Car Ramrod

    In BMW land it’s nearly always the hood sensor. You would know for sure by going through the diagnostic process Sajeev suggests, but the hood sensor should be a relatively cheap and easy replacement to try first if you don’t have much time.

  • avatar

    Sensors be dammed. Why…anyone knowing there’s a warmer climate but stays put, is beyond my ability to comprehend.

  • avatar

    Please don’t listen to anyone telling you to sell it. You drive one of the most reliable SUVs on the planet. Here in Pennsylvania (cold weather) I do routine service on plenty of these and see no major problems, unlike all the timing chain guides I replace on GM products, and pulling lists of codes a mile long out of German vehicles. Sajeev is probably right about the sensor, but like THX1136, I would lean toward the door sensor, as it has been open and closed many more times than the hood. (If this were a BMW, then it might very well be the hood sensor, since the hood is opened and closed on one of those vehicles much more often than the driver’s door is opened, lol.) Take it to a competent mechanic, get an accurate diagnosis, pay for the repair, and enjoy many more miles of trouble-free driving!

    • 0 avatar

      My wife’s aunt did. Not worth driving thr clunker in the city with hot and and not top crash ratings.

    • 0 avatar

      Thanks Yankee.
      I don’t intend to get rid of her. She’s been a great car!

      My son has a Honda Civic, 1996, with 350,000 miles on it. You couldn’t pry it from his cold dead fingers. He is President of his own high mileage Honda club.

  • avatar

    A ‘fob’ is only capitalized if you’re in the freight business, where it means Freight On Board. Otherwise it’s just a regular old noun.

  • avatar
    Uncle Mellow

    Does the vehicle have hands-free-telephone ? Does it work ? When the HFT module dies ( average 10 years ) it drains the battery 24/7 and that can set off the alarm in the middle of the night.

  • avatar

    If you’re looking for the easy answer, zero dollars spent, it ain’t happening. Not that it’ll cost much to fix, but clearly you don’t know anyone that’s handy with wire snips or test light. Any repair or stereo shop will do.

    It’s an older car and there’s really no need for so many sensors/triggers, if you must have an alarm. By the time anyone opens the hood or hatch, the shock/motion, glass sensor or dome light should’ve lit up.

  • avatar

    Agreed that it is a door sensor.

    I’m guessing its the driver door that gets opened and closed to reset the problem. I’d just order a new switch and replace. The slamming of the door probably resets the switch just enough to work.

    A suggestion to verify, leave both front and rear dome lights on the door open setting (turns on when the door is open) and when it goes off again, see if the dome light is on.

    My wife’s CRV had an issue with the battery draining, found out that the rear hatch switch wasn’t closing all the way (due to collision damage) and that even though there was no bulb, the computer kept something on. If you opened and closed the door, it would shut the switch for a moment, enough to turn whatever it was off. What had me scratching my head, until I found it was that some nights it would kill the battery, other’s it wouldn’t. And it all had to do if the trunk got opened and closed after turning the vehicle off.

  • avatar

    I this was a VW, it would definitely be the door-sensor microswitch; they wear out with these symptoms.

  • avatar

    I this was a VW, it would definitely be the door-sensor microswitch; they wear out with these symptoms.

  • avatar

    The factory alarm is not activated by the door pin switches, it is activated by the internal switches in the door latches. If the body module senses a door unlock, without the key fob or key being used. it sounds the alarm. Most likely on this vehicle, one of the door lock actuators (which are part of the door latch assy) is seizing, which causes the internal switch in the latch to trigger. Easiest way to check is to manually lock/unlock each door with the inside knob. If you feel one or more difficult to lock/unlock, replace that latch assy. There is a safety recall for the LF latch/actuator, so if it’s that door, it may be covered by Honda.

    • 0 avatar

      This makes sense – because if I break into your car, I’m going to *unlock* the door before I open the door (whether I break the window or use a lockout tool or use a wedge to reach the lock switch).

      Diana, how old is the battery? A relatively weak battery which gets even weaker in colder temperatures would be the simplest explanation tying the alarm to freezing temperatures. As Sajeev suggested, many automotive parts stores will test your battery for free.

      IF the battery is good, set the alarm (lock the doors with the fob) from outside the vehicle and pull on the hood and then the liftgate (the same way that ice/snow might push up/out on them as it gets colder and the ice expands). Does that set the alarm off? (If it is the rear liftgate, check for dirt/debris in the rear liftgate seal, clear it out and try again.)

      Now try the same thing with each of the doors (from outside the vehicle).

      Then, sitting *inside* the car, set the alarm by locking the doors with the fob, and then try poltergeist’s tip of manually unlocking each door and setting off the alarm [we think] – does one of them feel different from the others or set the alarm off more ‘quickly/easily’?

      Interestingly, the front right (passenger side) and rear right Door Lock Actuators are some of the most popular parts sold on (denoted by the little heart symbol) for the 2008 CR-V:,2008,cr-v,2.4l+l4,1441752,body,door+lock+actuator,13257

      [If it turns out to be one of the door lock actuators and you do the repair yourself, be careful doing it in the cold – the plastic door panel parts you need to remove will be more brittle in cold weather.]

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