QuestionHello John;
On a recent long distance trip down to Los Angeles from Victoria, BC' - my 4.0 Litre GEMS Disco engine started to 'feather' at hi-speed (70 mph) - particularly as it got warmer in California. The first code it threw at me was a PO???? (I have the number written down elsewhere I did check it in my code book and it was concerned with 02 sensors) concerned with too lean a value coming out of the Mount Shasta area and it was then that I got the feathering at hi-speed; the next code was a P1176 thrown at me a few days later and finally today a P1179. The earlier codes went away on their own without me pulling them ! LR in Santa Barbra thought it the P1176 was concerned with the Mass Air Sensor - as that has been their experience or they thought it could be the vehicle speed sensor (is there such a thing?)?
I changed a splugged fuel filter in LA and I have poured through a lot of fuel systemn cleaner and that has helped quite a bit.
perplexed any ideas?
Geoff
AnswerHi Geoffry,
P1176 is upstream O2 sensor related.
MAF is expensive part to swap - especially if you are not certain.
P1179 usually is associated with MAF...you can try to avoid buying a new one by using electrical contact cleaner on the harness. Remove the MAF and give it a careful cleaning. One owner even looked into the abyss and cleaned the inside contacts that were covered in black soot.
I've heard other owners solving this problem by cleaning the connections. I hope it works for you too.
Best of luck,
JohnMc
Here's an article I once read (thanks Chris S.L):
An intermittent VSS fault is identified by a freeze frame speed of above 110 mph (an input to GEMS caused by a noisy signal from the VSS), complaints of intermittent power loss, or engine stall.
NOTE: On TestBook disc DRG 0001 and DRG0002 the road speed displayed as "MPH" is actually a kilometers per hour value, NOT miles per hour. A TestBook reading of "177 MPH" is actually 177 kph. This reading, when converted to the desired mile per hour reading, is 110 mph.
One of the functions of the VSS signal to the GEMS unit is to provide information on vehicle speed. If the GEMS unit sees an excessively high speed (above 110 mph) it will initiate fuel cut off to the odd cylinders momentarily to reduce engine power. This feature is intended to prevent the driver from operating the vehicle at excessive road speeds.
Customer complaints of intermittent engine surging at highway speeds, inoperative or fluctuating speedometer, or a MIL illumination could be caused by an intermittently failing VSS.
If the MIL is illuminated with misfire codes P0300, P1316 and any combination of P0301, P0303, P0305 and P0307 stored or if the customer complaint is surging, hesitation, or loss of power at highway speeds, pay close attention to the freeze frame data, particularly engine rpm and road speed.
NOTE: As with all electrical diagnosis, the circuit between the sensor and the GEMS unit should be checked. The technician should be aware of the fact that the sensor test will not detect an intermittently failing sensor.
If the freeze frame data shows a road speed that does not conform to the engine speed (for example 110 mph at 2000 rpm or a road speed of 0 mph), an intermittent fault with the VSS could be the problem.
If inconsistencies between engine speed and vehicle speed are observed, replace the sensor. See attached DTCR samples
