94 K2500 Suburban 6.5L Code 78 [Archive] - TheDieselPage.com Forums

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PerryMo

12-19-2003, 19:20

Have any of you guys experienced an sporadic Service Light. Light comes on during moderate acceleration only. Only code is 78. Any ideas?

whatnot

12-19-2003, 20:39

It is most likely the wastegate solenoid, the vacuum pump or a broken vacuum line.

PerryMo

12-20-2003, 02:06

Thank you. Any easy way to test the solenoid?

whatnot

12-20-2003, 21:19

You should be getting vacuum at the wastegate line with the engine idling. If there is none, then check the line to the solenoid (from the vacuum pump). If there is vacuum there, it is probably easiest to just replace it since it doesn't cost that much.

PerryMo

12-21-2003, 16:39

Thanks for the info. I saw an article on the site pertaining to this problem. I will order a reprint of the feature articles if this does not work.