Shift light
Race Director
Joined: Aug 2007
Posts: 11,889
Likes: 8
From: Whitefish Falls Ontario
St. Jude Donor '08-'09
IIRC all C4 6 speeds were equipped with the skip shift feature, from most posts on the subject it has been eliminated.. The kit for this doesn't get rid of the light though..
Race Director
Joined: Oct 2005
Posts: 11,769
Likes: 175
From: Rolla Missouri
2021 C4 of the Year - Unmodified Finalist
St. Jude Donor '10 thru '25
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 41
From: Baltimore, MD USA
90 Service Manual says, in vehicles equipped with a Manual transmission,
a bulb lights when the car should be shifted to
the next higher gear for better fuel economy. Battery voltage
is applied to one side of the bulb. The other side
of the bulb is switched to ground by the ECM which
uses engine data such as rpm, vehicle speed and intake
vacuum to compute an efficient shift point.
The diagram even shows an overdrive bulb for automatic transmissions.
The 1990 owners manual only says this for a manual transmission.
For a L98 Vin 8 vehicle you have an up shift light on your instrument
panel. This light will remind you to up shift to Sixth gear during cruising.
If you have a ZR1, this light will also indicate the up shift point for optimum acceleration during wide-open throttle maneuvers.
Whether this up shift bulb function was actually implemented in the eprom firmware code
I've posted a diagram showing the up shift bulb position in the dash cluster if you want to verify it's there and not burnt out.
Last edited by Hooked on Vettes; May 7, 2014 at 10:26 AM.
Thread Starter
Advanced
Joined: Dec 2010
Posts: 64
Likes: 0
From: Orange So Cal
The ECM has the circuitry to drive the Up shift bulb in the dash cluster.
90 Service Manual says, in vehicles equipped with a Manual transmission,
a bulb lights when the car should be shifted to
the next higher gear for better fuel economy. Battery voltage
is applied to one side of the bulb. The other side
of the bulb is switched to ground by the ECM which
uses engine data such as rpm, vehicle speed and intake
vacuum to compute an efficient shift point.
The diagram even shows an overdrive bulb for automatic transmissions.
The 1990 owners manual only says this for a manual transmission.
For a L98 Vin 8 vehicle you have an up shift light on your instrument
panel. This light will remind you to up shift to Sixth gear during cruising.
If you have a ZR1, this light will also indicate the up shift point for optimum acceleration during wide-open throttle maneuvers.
Whether this up shift bulb function was actually implemented in the eprom firmware code
I've posted a diagram showing the up shift bulb position in the dash cluster if you want to verify it's there and not burnt out.
90 Service Manual says, in vehicles equipped with a Manual transmission,
a bulb lights when the car should be shifted to
the next higher gear for better fuel economy. Battery voltage
is applied to one side of the bulb. The other side
of the bulb is switched to ground by the ECM which
uses engine data such as rpm, vehicle speed and intake
vacuum to compute an efficient shift point.
The diagram even shows an overdrive bulb for automatic transmissions.
The 1990 owners manual only says this for a manual transmission.
For a L98 Vin 8 vehicle you have an up shift light on your instrument
panel. This light will remind you to up shift to Sixth gear during cruising.
If you have a ZR1, this light will also indicate the up shift point for optimum acceleration during wide-open throttle maneuvers.
Whether this up shift bulb function was actually implemented in the eprom firmware code
I've posted a diagram showing the up shift bulb position in the dash cluster if you want to verify it's there and not burnt out.
There must be something in my program then that keeps it from working.
I am using the AXCN broadcast code bin file.
Thank you.
Team Owner
Joined: Sep 2003
Posts: 25,366
Likes: 2,733
The ECM has the circuitry to drive the Up shift bulb in the dash cluster.
90 Service Manual says, in vehicles equipped with a Manual transmission,
a bulb lights when the car should be shifted to
the next higher gear for better fuel economy. Battery voltage
is applied to one side of the bulb. The other side
of the bulb is switched to ground by the ECM which
uses engine data such as rpm, vehicle speed and intake
vacuum to compute an efficient shift point.
The diagram even shows an overdrive bulb for automatic transmissions.
The 1990 owners manual only says this for a manual transmission.
For a L98 Vin 8 vehicle you have an up shift light on your instrument
panel. This light will remind you to up shift to Sixth gear during cruising.
If you have a ZR1, this light will also indicate the up shift point for optimum acceleration during wide-open throttle maneuvers.
Whether this up shift bulb function was actually implemented in the eprom firmware code
I've posted a diagram showing the up shift bulb position in the dash cluster if you want to verify it's there and not burnt out.
90 Service Manual says, in vehicles equipped with a Manual transmission,
a bulb lights when the car should be shifted to
the next higher gear for better fuel economy. Battery voltage
is applied to one side of the bulb. The other side
of the bulb is switched to ground by the ECM which
uses engine data such as rpm, vehicle speed and intake
vacuum to compute an efficient shift point.
The diagram even shows an overdrive bulb for automatic transmissions.
The 1990 owners manual only says this for a manual transmission.
For a L98 Vin 8 vehicle you have an up shift light on your instrument
panel. This light will remind you to up shift to Sixth gear during cruising.
If you have a ZR1, this light will also indicate the up shift point for optimum acceleration during wide-open throttle maneuvers.
Whether this up shift bulb function was actually implemented in the eprom firmware code
I've posted a diagram showing the up shift bulb position in the dash cluster if you want to verify it's there and not burnt out.
Last edited by WVZR-1; May 7, 2014 at 06:03 PM.
