Totenhofer Posted February 20, 2018 Share Posted February 20, 2018 Hey guys, just purchased a 1999 Mack ch fleetliner with a 470 and Mack 18 speed cant seem to find any information on this topic, the speedo has just randomly decided to stop working and now it feels underpowered only light on the dash is electronic fault. And what boost do the early 470s make it’s just always felt underpowered from the start. Quote Link to comment https://www.bigmacktrucks.com/topic/52572-mack-ch-470-no-speedo-underpowered/ Share on other sites More sharing options...
Jamkar Posted February 20, 2018 Share Posted February 20, 2018 Gday mate, welcome aboard. If the speedo sensor fails or gets dirty the the truck will derate. Should see 32ish psi. With engine idling, cruise off, hold speed set button down until light starts flashing and count how many times the yellow light flashes. Should give you 2 groups of flashes/numbers. Let us know. Quote Link to comment https://www.bigmacktrucks.com/topic/52572-mack-ch-470-no-speedo-underpowered/#findComment-392477 Share on other sites More sharing options...
Totenhofer Posted February 21, 2018 Author Share Posted February 21, 2018 Hey mate thank you so much for the advice, ok so replaced speed sensor, completely different truck to drive, base of the sensor was all broken away looks to have been screwed in to far. is now running at around 29/32 psi boost so was definitely derated. So I tried what you said with the cruise control, the electronic fault light flashes 4 times then goes out for a second then flashes once then goes solid again. So the sequence is 4.1If that makes sense, and it does that every time I hold down the set/deceleration button. Thank you again Sam. Quote Link to comment https://www.bigmacktrucks.com/topic/52572-mack-ch-470-no-speedo-underpowered/#findComment-392553 Share on other sites More sharing options...
hatcity Posted February 21, 2018 Share Posted February 21, 2018 4-1 is vehicle speed sensor...you replaced and all is good malfunction lite should go out Quote Success is only a stones throw away.................................................................for a Palestinian Link to comment https://www.bigmacktrucks.com/topic/52572-mack-ch-470-no-speedo-underpowered/#findComment-392557 Share on other sites More sharing options...
Totenhofer Posted February 21, 2018 Author Share Posted February 21, 2018 Cheers mate. noy sure why it was still flashing 4.1, now it’s changed I reset the isolation switch on the truck, it’s flashing 7.2, 7 times then 2 times. do we know what the combination means? thanks guys Quote Link to comment https://www.bigmacktrucks.com/topic/52572-mack-ch-470-no-speedo-underpowered/#findComment-392588 Share on other sites More sharing options...
hatcity Posted February 22, 2018 Share Posted February 22, 2018 7-2 is "parking brake switch" Does park lite come on, on dash when applied? also, do the brake lites work with low air. on mine, the brake lites stayed on until about 80 psi Quote Success is only a stones throw away.................................................................for a Palestinian Link to comment https://www.bigmacktrucks.com/topic/52572-mack-ch-470-no-speedo-underpowered/#findComment-392593 Share on other sites More sharing options...
Totenhofer Posted February 22, 2018 Author Share Posted February 22, 2018 Cheers, Yeah park brake light is always on the dash, and yeah brake lights will come on with low air sometimes , is it a sensor that controls this or the actual park brake switch itself? thanks. Sam Quote Link to comment https://www.bigmacktrucks.com/topic/52572-mack-ch-470-no-speedo-underpowered/#findComment-392679 Share on other sites More sharing options...
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