A new €100 million Garda digital radio system has been found to be incompatible with electronic breathalyser kits.
The portable breath-testing kits were withdrawn from the Dublin area last year after it emerged that signals from the new Tetra digital radio system adversely affected breathalyser readings.
However, a Garda spokesman said that the proposed random breath-testing would not be affected by the problems.
The Tetra system, which will cost €100 million, was rolled out in two Dublin divisions on a trial basis in 2001.
In early 2002 it emerged that readings from portable electronic breathalyser kits could be affected by the Tetra signals.
According to a spokesman for the Garda, the electronic kits were withdrawn from the Dublin area in March 2002 as soon as the problem emerged.
The problem is being examined by the Medical Bureau of Road Safety, according to the spokesman.
In the meantime gardaí in the Dublin area have reverted to using the older "blow-in-the-bag" kits, while colleagues around the country use the electronic kits.
He said it would have no effect on the ability of gardaí to secure drink-driving convictions or to enforce the random testing measures to be introduced in time for December.
Like the blow-in-the-bag, the electronic kit was used as an indicator for gardaí as to whether an individual might be over the alcohol limit.
"It is not used for evidence purposes," the spokesman said. As such it would have no impact on random testing either.
Suspected drink-drivers are all arrested and taken to a local Garda station where they provide blood or urine samples or are tested using the new intoximeter machine.
The machine is unaffected by the Tetra system and was seen as being necessary before random testing could be introduced, as it can process a high number of tests compared with blood or urine samples.
Its use had been held up by legal challenges until earlier this month when the High Court dismissed a challenge to the intoximeter from seven people, who claimed that they should have been able to inspect it.
Up to 2,000 drink-driving cases are in the District Court system awaiting the outcome of legal challenges to the intoximeter.