Hi Guys,

I have a 1994 saturn sl-2 that has a check engine light and the spedometer and miles gauge dont work. i put ob1 computer on it and it is reading codes 26, 27 qdm fault. i put a new speed sensor in and the speedometer still doesnt work.
any answers will helpful thanks jeremy.

 

Well, if your OBD 1 had reported a "code24", I would have agreed to your decision to replace the VSS. However, you report codes "26 & 27", which are quad driver module faults. Remember, the VSS signal goes to the PCM, and the PCM actually drives the speedometer.

Based on your report, I'd opt for a replacement PCM

 

I replaced the pcm today and still have the codes 26,27 and no speedometer and a check engine. i paid 318.00 for the computer. i already changed the speed sensor.

 

quad driver fault codes are almost never from actual quad driver failure

from one of my earlier posts-----
Originally Posted by derf
code 26 (quad driver output fault) is almost never the actual quad driver within the PCM itself; it is almost always something hanging off that circuit. This circuit is used to simultaneously monitor the status of

SES circuit
Coolant Hot light
cooling fan relay
A/C clutch
Speedometer Cutout
Upshift/Shift to D2 light
EGR solenoid
Canister purge solenoid

Diag in the order listed.
______
My personal guess is that the issue lies between the VSS and the speedo odo electronics or on the speedo circuit board in the cluster itself


Note:

does your car have the passive restraint system (motorized seatbelts)? do they operate properly?

I ask because the VSS signal is routed through the PRM on these cars -- if the PRM fails it often hoses the VSS signal on its way to the electronics that drive the speedo and odo.

 

These codes are defined as a quad driver output fault. In general, any of the outputs from the PCM or Performance Control module. A 26 is a shorted or open circuit, a 27 is an intermittent problem. This is a general statement applied to any of these outputs.
The VSS signal is generated by a Permanent magnet generator mounted in the transmission and is sent to and monitored by the Performance Control Module and translated into vehicle speed which is in turn sent to the Instrument cluster and used by the separate Speedometer and Odometer electronic circuits used in the instrument cluster.
It is also used by the cruise control.
If you have cruise control and it is functional, then probably everything is working up to a point and your problem lies with the instrument cluster and it's subassemblies.
If Cruise Control also does not work than it is a bit of guess what is going on but assuming that all symptoms are related then it appears to be a wiring problem coming off of the Performance Control Module and if not a specific wire problem could be a connector being corroded. If all symptoms are not related than you may have more than one problem. Assuming not catastrophic, still check connectors if you can for corrosion. Plugging and unplugging is usually all that it takes to solve these. The guess would be damaged wiring somewhere if something other than a connector. If cruise control also does not work. The damage most probably between the Performance Control Module and everything else such as cruise and instruments.

 

Hey all, I'm new here. I joined because I saw that Mr. Jeremy had the exact same problem and saturn that I have. My speedometer and odometer do not work (neither does my cruise control, I'm only assuming this is related), and my "service engine soon" light is on. This happend at the same time. Checked codes (26, and 27 qdm error and qdm fault). VSS appears to work. I can observe speed on a geneses scan tool while driving, yet unable to read speed on instrument cluster. I understand each quad is responsible for 4 outputs, giving 8 possible output failures. I seem to have 7 out of 8 working correctly. I've removed the instrument cluster to observe wire connections to no avail. I've also checked every fuse... also to no avail. I feel the problem is either the cluster, the quad driver, or the circuitry connecting the two. I have not been able to find adequate wiring diagrams. Please help.

PS. Can the EVO on the power steering cause this?

 

I was just going to look the drawing up when I realised I already addressed this a year ago on the post just before yours. #5. On my car where the odometer does not function at all but the speedometer AND cruise control does work the problem on mine is with the cluster.
If you have a failure of all of the above and can read things using a scan tool, the problem is not the generator of the signal as it must be being generated if you can read the results of it with a scan tool, but a bad connector (probably) where it connects into something sending the signals required to both the cruise control and the instrment cluster.
The wiring diagrams I have are basic and included in the Mitchels, Chiltons or whatever paper back generic fix your Saturn books available in the help section of places like O'Reilys or Advance or other auto parts stores.

 

After reading the above posts, is it recommended that I try to fix a non working cruise contol. I have a SL 01 with 85,000.